Overtook the Manga

"Mokuba: We appear to be locked on course with a giant ocean fortress directly beneath us! Yugi: That's weird. I don't remember any of this happening in the manga."

- Yu-Gi-Oh!: The Abridged Series

Many Anime are based on a Manga—the Japanese equivalent to comic books. While simply making the anime into a completely Alternate Continuity is common, especially if the manga has No Ending, more often the anime at least tries to follow the major plot points of the original manga.

If a series is especially popular (and/or marketable), though, its anime version will begin before the manga even ends. Because of medium conventions, it takes longer for events to unfold in manga than it does in anime, the average conversion being roughly 2 manga chapters to make 1 anime episode, and this often means that an anime will simply run out of source material. While some manga series are published weekly (e.g., Shonen Magazine/Sunday/Jump, etc), others are published on a monthly schedule (e.g., Nakayoshi, Shonen Ace). However, most anime are aired weekly, which just makes it worse, especially for manga that have just started. The producers of the anime are then in a fix. They can't just wait for the mangaka to produce more material because they have a broadcast schedule to meet. Japanese shows are almost always broadcast solely as first-run episodes with no reruns. No new episodes is akin to being canceled. This is something that is frequently Lost in Translation outside of Japan, since unlike Western shows, they don't schedule production in the form of "seasons" with production breaks set into the schedule. They just keep going and going and going or stop at a predesignated point. This is also why lots of anime are only 12 or 24 episodes long, because that's all they were scheduled for, regardless of popularity.

Unless they work in very close tandem with the writer of the original manga, which is very rare since they're usually really busy with the manga as it is, so the people in charge of the anime will thus have to start making things up on their own, and create a unique plotline from the point they ran out of manga to base things on.

Unfortunately, unpopular or unwelcome filler arcs or filler episodes may often be Misblamed as being the fault of the author(s), when in reality, they may often not have a whole lot to do with the filler plot. Some fillers that were better received by fans are often cited as being opportunities to develop lesser characters. (This often helps with anime that have a cast size near the size of the production staff.)

Another option could easily be to just pad the episodes out and slow the story down. This was common in the Dragon Ball series, which unfortunately caused many people to believe the manga was exactly the same or that Akira Toriyama's writing was at fault; when the pace of the anime was out of his hands.

Most writers just choose to do a Gecko Ending instead.

See also Wacky Wayside Tribe.


 * Ai Yori Aoshi. While Ai Yori Aoshi and Ai Yori Aoshi Enishi follow the manga for the most part pretty faithfully, its ending accomplishes nothing story wise.
 * This happened to Blue Exorcist. It followed the manga pretty well up until the very first filler episode, after which they both went in two entirely different directions. Some fans are not pleased.
 * Bleach created the Bount Arc.
 * During the Hueco Mundo arc they had to insert more Filler, the only problem, was that there was no room to insert filler, so the entire arc takes place post-Winter War. Which would ruin the suspense, if it were possible for named characters in Bleach to ever die, anyway.
 * Because of Kubo's incredibly slow pacing in the more recent arcs, the anime has actually stopped for another filler arc. That is the second filler arc in this story arc, not counting the stand alone filler episodes. The characters themselves actually lampshaded this, asking the viewer to bear with them. Luckily, it seems to actually be fairly popular.
 * Likely for this reason, Bleach has been put on a year long hiatus on March 27, 2012, as the manga entered the final arc.
 * The Bokurano anime was completed before the manga was, resulting in the last half of the anime having absolutely no connection or resemblance to the equivalent in the manga, with the exception of one plot twist that the manga author might have decided to use after the anime came up with it.
 * The different direction the anime took wasn't just due to the fact that it Overtook the Manga, given this
 * Also, Kitoh included hints to said plot twist in the manga before the anime introduced them, so it's safe to say he informed Morita of the twist instead.
 * In Chrono Crusade, the anime took a radically different direction from the manga in the last third of the series. Whether or not this is necessarily a bad thing is up to you.
 * Dragon Ball has three notable points that were to let the manga material get ahead for a few weeks: Goku's travels across the Earth following the defeat of the Red Ribbon Army and wishing Bora back to life, Gohan, Piccolo and Krillin's encounter with Garlic Jr. and Goku competing in the Other World Tournament.
 * The filler after the Red Ribbon Saga is especially notable in that it was actually properly set up by the manga. In the last chapter of the Red Ribbon Saga, Master Roshi tells Goku to continue training by travelling around the world and that while, travelling around the world, Goku will have many adventures and a lot of fun. In the next chapter of the manga, there's a time skip and Goku has already completed his journey around the world, the adventures mentioned by Master Roshi are never shown in the manga. This whole sequence is basically the manga giving the anime an excuse to do a series of filler episodes.
 * Excel Saga outright went for an entirely different storyline to avoid such a scenario. To wit, the original manga gets considerably darker (though still very satirical) a few volumes after the adapted-to-anime material ends.
 * The Eyeshield 21 anime has a lot more wacky hijinks between games because of this.
 * The first part of the Fist of the North Star TV series had many drastic changes to the order of events as a way of preventing it from getting ahead of the original manga. Kenshiro's battle with Shin was pushed back to the end of the first part, numerous one-shot villains were introduced, and several other villains from the manga, namely the Godland Colonel and Jackal, were shown to be working for Shin. The subsequent parts also featured Filler, but generally kept the main storyline going in the same order.
 * The 2003 anime adaptation of Fullmetal Alchemist went into an Alternate Continuity from its very early episodes, although the changes were fairly subtle in the beginning. This is because the creators knew in advance that it would overtake the manga, as did the manga's creator, who explicitly asked them to take this route.
 * Averted with the second series, Fullmetal Alchemist: Brotherhood which revealed it was sticking with the manga ending - the final episode was aired about two weeks after the final manga chapter was released.
 * Gantz is an odd example. The manga and anime were created at about the same time. The animators, knowing they would eventually get ahead of the manga, decided from the beginning that it would only follow the manga through a few arcs. The anime ended with an arc that was nowhere in the manga.
 * The anime version of Great Teacher Onizuka followed the manga for the most part right up the trip to Okinawa.
 * Averted in Guyver, which has had three animated adaptations and none of them have gone past the first appearance of Guyver Gigantic. This happened in the early 90s... and the manga is still ongoing. Even the most recent anime, produced in 2005, just barely got Guyver Gigantic in. Many Guyver fans would love an anime that runs long enough to overtake the massive manga lead...
 * .hack//Legend of the Twilight also diverged from its manga once it reached the "Haunted House." This included, oh, removing half to all of the plot. To this day, the Twilight anime is the only installment, besides the gag OAV .hack//GIFT, which does not count officially in the series canon.
 * Hellsing's creator was very upset when the anime went a completely different direction with characterization in its "Incognito Arc". Further adaptation of the comic was postponed for years. An OVA much more in line with the original is underway with the ninth episode in production.
 * Eh, the story has always been radically different with (back then) comic relief Seras Victoria promoted to audience surrogate and different characterization. Plus Hirano wasn't upset at all, he lists the Anime as "cool" in volume 10. And in an interview, he says he likes the anime because "it has its own identity." And the series was only supposed to be 13 episodes. All the official Gonzo interviews and material (including a guidebook) say it was concluded. The ending was meant to be ambiguous like the Manga was.
 * Despite this happening, Hunter X Hunter has at most four episodes that could be considered filler in it, and they were all fairly early on. Instead of making filler episodes, the anime simply stopped making episodes until the manga made significant progress, which is why it has three OVA seasons and stops at the end of the Greed Island arc. Whether or not more episodes will be created once the Chimera Ant arc finally ends has yet to be revealed.
 * The series has now been rebooted.
 * Inazuma Eleven is a rare example of the anime staff avoiding filler by working closely in tandem with the creators of the source material (in this case a video game series instead of a manga series). Whenever this happens, the anime simply starts on the plot of the next game before the game itself is released. The game series itself simply has its major plot points planned out well in advance; the 4th game, Inazuma Eleven GO, is currently scheduled for a winter 2011 release, but trailers had already surfaced a whole year in advance in December 2010. As a result, the major plot points are generally consistent between the game and anime, although plenty of details and smaller points differ.
 * When the Inuyasha anime series Overtook the Manga, Sunrise opted to simply end it, resulting in a finale that only gets about 7/10 the way through the story, and thus fails to resolve any of the major plot threads of the series.
 * However, Inuyasha the Final Act is a continuation of the previous anime, and covers the remaining volumes of the manga, since the series ended in 2008.
 * Kashimashi: Girl Meets Girl ignores a new plotline added in the manga and goes for a Gecko Ending—probably for the better, although opinions differ.
 * Because the anime version of Keroro Gunsou (a.k.a Sergeant Frog) frequently runs ahead of the manga (particularly in more recent years) a number of episodes and plots are present in the former that are not in the latter, such Karara's repeated appearances to marry one of the members of the platoon and the timer counting down to the invasion in season 3.
 * The anime version of Konjiki no Gash Bell (Zatch Bell in the West) ran at the same time as the manga version it was based on. Unfortunately, Makoto Raiku, the author of the manga, broke his hand, forcing the manga version to go on hiatus while the author's hand healed enough to allow him to draw again. The anime Overtook the Manga as a result, so the anime diverged from the manga for its final episodes.
 * Some aspects of the anime made it into the manga once Raiku resumed drawing, the most notable being.
 * The popularity of Black Butler caused it to be adapted way too soon, the anime wound up going in a totally different direction than the manga. Only 9 of the 24 episodes are adapted directly from the manga.
 * Mermaid Melody Pichi Pichi Pitch also had filler while waiting for the manga that eventually crowded out key plot points from said manga. Meaning? Anything involving Coco.
 * Naruto is perhaps the most infamous example since Dragon Ball. The show ended up with two entire seasons composed solely of episodic filler and nothing else. This (eventually) led to a severe drop in ratings, resulting in the time-jumped arc being essentially a relaunch with the new title of Naruto Shippuden.
 * Although in its defense, some of the filler arcs were quicker-paced and more action-filled than the show itself.
 * Also, some of the filler arcs are moderately popular for providing screen time to fan favorite secondary characters.
 * Waterfall episode, anybody?
 * The post-Time Skip filler arcs are somewhat liked for giving some attention to some otherwise under featured characters, expanding on the source material instead of just adding irrelevant side-stories that go nowhere, and being full Story Arcs instead of largely pointless 1-3 part episodes.
 * well they were but they seem to have gone back to stand alone episodes that even went so far as to flash back to the original Naruto series. Thus Shippuden now contains additional Naruto filler, greaaat.
 * Ouran High School Host Club pretty much averted this. The anime came out in 2006 and ran for only one season, while the manga, updated monthly, is still currently ongoing with over 70 chapters. Despite this, the anime followed the manga nicely with the exception of a few minor alterations that more or less didn't really affect anything. Only the very last two episodes or so drift from the manga. The anime ending was enough to give some closure, but still relatively open, leaving all pairings technically possible for fangirls to squee over.
 * Most shoujo stories published by Hakusensha seem to only receive roughly 26 episodes of anime adaptation (either a single series or two half-size seasons) which ends way before its manga source is anywhere near a proper conclusion. The production studios therefore don't have to wait for the manga at all provided it already has enough material for a one-season anime, and those who like the series can start reading the manga for continuation and/or more details. Whether this tactic actually works tends to vary between the series, though.
 * The anime Peacemaker Kurogane actually ends at the prequel for the actual manga "Peacemaker Kurogane", and only follows the events of the manga "Shinsengumi Imon Peacemaker". Sound confusing? It is.
 * While most of the Pokémon seasons are based directly off of one of the handheld video games, having Ash and co. visit the region of the currently-released installment and compete in the regional League, the second season, named "The Orange Islands", took place on a completely original set of islands. This was due to Pokémon Gold and Silver not yet being released at the time; while they could've had the characters potter about the Kanto region for another 35 episodes, moving the story to a more original setting allowed the producers to start introducing more of the new Johto Pokémon ahead of Gold and Silver's release.
 * The alternative of stretching out the original plot was done for all future blocks except one. Johto was the most infamous for this, with a dozen episodes passing before anything happened. The exception was the Battle Frontier arc, which combined the remakes FireRed/LeafGreen and Updated Rerelease Emerald to make an original arc about revisting Kanto.
 * This actually allowed Finnish MTV channel to remove Orange saga from their TV.
 * Ranma ½ overtook its manga source several times, and made a large number of episodes from scratch each time it happened.
 * Several episodes also were condensed arcs from the manga as well, but that may often be expected.
 * An interesting phenomenon was when an event in the anime and the manga happened at different seasons. When Ranma fights Cologne, it's a summer Beach Episode in the manga, whereas it's a winter ski trip episode in the anime. As a result, the two are quite different.
 * This ironically did not happen to Rosario + Vampire; the first season of the anime stopped about halfway through the first serialization of the manga, which itself was just getting into its second, but not only did they rush to release the second season anime within a few months of the first, but rather than picking up where they left off, they skipped the rest of the first serialization altogether and went directly into the second, which had barely been around for a year by then. The result is not well-liked.
 * Despite that, they used a lot of stories from the first serialization on the second season.
 * The Rurouni Kenshin anime's last three arcs—the Christian/Shimabara Arc, the Black Knights Arc, and the Feng Shui Arc—were anime-only, created while waiting for the author to finish the manga. The first arc was alright, albeit much less combat heavy than previosu ones, but this coupled with the lower quality of the other two led to the anime's cancellation and the final manga arc (the Enishi/Jinchuu Arc) was never fully animated.
 * Nearly half of the first-season episodes (almost everything after the end of the Oniwaban arc) were filler, largely consisting of stand-alone episodes or two or three episode storylines that were basically watered-down versions of other plots from the manga (the series and the movie have three or four low-rent versions of the series' ultimate Big Bad Shishio—masterminds with a vision of the "good old days" who gather together a bunch of unemployed swordsmen to embark on national conquest).
 * Sailor Moon invented mini-arcs in case new seasons weren't picked up or when they had to Snap Back after Overtaking The Manga, such as the mindwipe in the first season. This is particularly noticeable in SuperS, which shares almost nothing in common with its manga counterpart and is noted for having had a significant ratings drop in Japan, and for being most of the fandom's least favorite series. In the final season, they broke their rule of one Big Bad per season for a mini-arc that brought back the rest of the cast and properly ended the previous series by recycling the Big Bad of SuperS. After that arc, the proper Big Bad, Galaxia, showed up and the real plotline started.
 * The whole Doom Tree arc at the beginning of Sailor Moon R was created so that the mangaka could restart the manga (the original story was supposed to end with the defeat of Beryl) and get ahead of the animation.
 * Saint Seiya created the whole Asgard arc after the Sanctuary Chapter which surprisingly enough became one of the fans favorite arcs. On the other hand, they created several episodes in the Sanctuary Chapter which led to some confusions notably with the introduction of the Crystal Saint as Hyoga's mentor when it was later revealed in the manga that Hyoga's mentor was in fact the Aquarius Saint. It was handwaved by making The Aquarius Saint the mentor of the Crystal Saint who was still the mentor of Hyoga the Cygnus Saint, thus establishing some kind of "coherent" hierarchy.
 * Saiyuki has had a number of these. The second arc of Gensoumaden was an anime-only arc, although Homura (the arc's Big Bad) was designed by author Kazuya Minekura and took existing elements from the Prequel series Gaiden, also on-going. Then, the current plot of the sequel Reload, which is on-going, was halted while the author was sick. In order to keep production going, the anime took the existing plot and characters and went in a completely different direction with them. A very, very different direction. Thus, important continuing plot elements from the manga were completely left out and the anime finished without them- with no word on whether the manga's version of the arc will be animated at all. This also led to a huge shuffle-around of manga to anime plots, with the second manga plot taking place in the first half of Reload anime, and the second half of Reload taking place in another sequel anime, Reload Gunlock.
 * In Saki, the manga ended the regional tournament just a few days before it ended in the anime.
 * Shugo Chara seems to have just barely avoided this (at least for the moment).
 * The Simoun manga debuted in the January, 2006 issue of Yuri Hime magazine, at which time the anime version had already started production. The two tell different stories, albeit with the same background.
 * Not exactly the same, but the Sonic the Hedgehog Archie comics are a rare Western inversion; based on the Sonic the Hedgehog cartoon, it had tons of side-stories and original content during the show's run, and continued long after the TV show was canceled. The only ties it currently has to its original progenitor is the occasional comic adaptations of whichever Sonic video game is coming out at the time (from which both comic and manga derived from).
 * The Sonic X comic has done the same thing, with the Sonic characters being shown still living on earth in the comic long after the anime had sent them home.
 * Soul Eater is almost exactly the same as the manga with only a few minor alterations (and more Excalibur for some reason) up until episode 37  Some of these changes, though, can actually be considered to be quite awesome, so it's really up to the viewer to decide.
 * With Soul Eater it was inevitable as the series belongs to a monthly manga, and since anime are made for weekly showings. It was going to catch up pretty quickly regardless.
 * Trigun overtook the manga by a fair margin, though how it did so is a rather unique situation. In 1997, Yasuhiro Nightow had to deal with the abrupt end of the manga with the cancellation of the Shonen magazine where he was published. By the time he restarted it as Trigun Maximum in the Seinen magazine Young King Ours, Madhouse had already begun production on the anime. As a result, the anime quickly caught up and finished long before the manga did. In fact, Trigun Maximum continued for nearly 9 years after the anime ended, finally finishing in April 2007. From Volumes 2-3 of TriMax, including the equivalents of episodes 20-21, the manga takes new directions with plot and characters, while retaining parallels in the plot—sometimes revealed in the manga years later—that Nightow had probably intended from the beginning.
 * Nightow even references the anime with volume 12, which includes a four-page montage of practically every key character from each chapter, including characters that had only been seen in the anime.
 * Nightow is on record as loving the anime, and has also admitted that the anime influenced his own story, making Trigun something of a Recursive Adaptation.
 * With Tsubasa Reservoir Chronicle, apparently CLAMP is so upset that production company Bee Train had to resort to making stuff up because CLAMP took too long and too slow to tell their story (a common occurrence) that they've given the rights to make an OVA of their series to a different company.
 * The fillers did break several rules that CLAMP stories strictly abide by. Most egregiously, one episode had the heros using a wish to restore the dead to life. An immutable, unbreakable law of nature in the Tsubasa-verse is that the dead never come back to life, no matter what happens. Hell, it ends up being one of the central themes of the entire story.
 * Venus Versus Virus's anime went in a completely different direction from the manga from the first episode. It also had a Gecko Ending.
 * Violinist of Hameln found themselves so far ahead of the manga that they needed to come up with their own explanations for many of the Chekhov's Gun found in the series, as well as creating a Gecko Ending for it all.
 * The Animated Adaptation of CLAMP's X 1999 have obviously counted into this because the manga was actually canceled (Or rather, it has been listed as "on Hiatus" for a long while) due to Monthly Asuka growing concerned about the manga's rather violent storyline and imagery present in the storyline, and the authors actually didn't want to be censored so they opted for hiatus. (Of course, the manga was actually pulled a couple times already for similar reasons.
 * Yu-Gi-Oh! loves to do this; the Virtual World (which occurred right in the middle of another in-manga arc), Doma / Waking the Dragons and the KC Grand Prix were a result of this. If nothing else, the Virtual World arc gave us more backstory on the Kaiba brothers.
 * The anime got through three whole arcs that weren't in the manga before they both finally rounded everything up in Millennium World.
 * Yumeiro Patissiere's anime will continue in October with a new season called Yumeiro Patissiere Professional, which will take place several years later with Ichigo now in high school. Since the manga, which is serialized monthly, is still in the middle of the first story, it's safe to say everything in the new anime will be new material.
 * This happened to Karin, resulting in a very anti-climactic yet funny ending for the anime and an elaborate Tear Jerker ending for the manga.
 * Daily Lives of High School Boys, despite a Slice of Life comedy, got this treatment due to two factors: (1) the manga's Sketch Comedy format means a whole volume of manga can only produce 3 episodes of anime without padding, and (2) Sunrise did not pad. The anime practically ran out of original material at the last episode; in which they asked the mangaka to draw two skits for the anime (High School Boys and Assertiveness and High School Boys and Getting Hit On) and made two original skits (High School Boys and ... and the faux High School Girls are Funky--The Movie trailer). Of course, being a ongoing Slice of Life manga without much of a plot, the anime simply ended the season by using Book Ends.
 * Dororo was never finished, which means all four adaptations go in completely different ways.

Film

 * The Jurassic Park novel series ended with The Lost World, so the movie Jurassic Park III was created from whole cloth. Following the Author Existence Failure of Michael Crichton, this will remain the case for any future film sequels.

Literature

 * Some of the early Star Wars Expanded Universe material that was published between the movies of the original trilogy, notably Splinter of the Minds Eye. It was written as a sequel to the first movie, but published when it was unknown if The Empire Strikes Back was ever going to be made. The Marvel Star Wars comic book series fits this trope to a tee despite ironically being a comic book adaptation of a screen franchise. First it adapts the first movie, then it has a bunch of original stories, then it adapts the second movie, followed by more original stories, then the third movie, and then it Overtook the Series.
 * S.D. Perry wrote a follow-up to her Resident Evil 2 novelization titled Resident Evil: Underworld, in which Sherry Birkin is left under the care of her heretofore unseen aunt, while Leon and Claire go on a new adventure with Rebecca Chambers and the surviving members of the Exeter branch of S.T.A.R.S. However, this book proved to be hard to reconcile when Resident Evil 3: Nemesis came out, as it revealed the fates of various characters after 2, which differed to what Perry came up with in Underworld. Perry had to explain away all the continuity snarls in her Nemesis and Code: Veronica novelizations.

Live-Action TV

 * All Creatures Great and Small: the show eventually ran out of James Herriot novels to adapt and started creating the scripts out of whole cloth.
 * The Showtime series Dexter had its first season based on the first Dexter book, Darkly Dreaming Dexter. The second season showed an original storyline as the second book, Dearly Devoted Dexter, was considered inappropriately dark for the show. There were no more books by the time the third season was greenlit, and since then the novels and TV series have gone their separate ways.
 * HBO's Game of Thrones series has one season every year. It's based on George R. R. Martin's A Song of Ice and Fire books, which provide enough material for one season each, possibly two if the screenwriters stretch it, but come out roughly once every five years or more. David Christopher Bell of Cracked.com calls this one of 4 Behind-the-Scenes Problems That May Kill 'Game of Thrones', and he suggests that the series may end up slipping into an Alternate Continuity. But after the first season of this slippage had aired, Felix Clay called it one of 4 Badass Works Of Art That Shouldn't Exist.

Video Games

 * The Tim Burton Batman movie was adapted to an NES game by Sunsoft, who took great liberties with the plot of the movie but still managed to churn out a pretty good sidescroller. However, Sunsoft couldn't wait for the next movie to come out before making a sequel to the NES game, and created Batman: Return of the Joker by themselves.
 * A similar example occurs with the SNES adaptation of Jurassic Park. Ocean couldn't wait for the sequel (or even the novel it would be loosely based on) and created their own, Jurassic Park 2: The Chaos Continues. It had a vaguely similar plot to the eventual sequel; a rival genetics company tries to take control of the island by force, and Alan Grant is sent to stop them. Nobody stopped to question why Grant was suddenly a gun-toting Contra-esque mercenary... or why he'd care about any of this. Good music, though.
 * Street Fighter was another interesting example in that Tiertex, the company responsible for porting the original Street Fighter to home computers (who also did a terrible job at at it) decided they couldn't wait for Street Fighter II to revolutionize the fighting game genre, so they took their port of Street Fighter and made their own original sequel to it, titled Human Killing Machine (which was also quite crap).
 * Years before Capcom released Strider 2, the official arcade sequel to the original Strider, they handed the Strider license to U.S. Gold and Tiertex (the companies that produced the European computer ports of the first arcade game) to produce their own sequel titled Strider II (spelled with a Roman numeral). This sequel was originally made for the same set of European computer formats and then remade for the Sega Genesis and Game Gear, getting a stateside release in the form of Journey from Darkness: Strider Returns.
 * When Konami wanted to make a sequel to Metal Gear following the success of the NES port in North America, they commissioned one of their teams to make a sequel specifically for the American market, resulting in the creation of Snake's Revenge. This inspired Kojima to make his own sequel for the MSX2, Metal Gear 2: Solid Snake. Snake's Revenge is not considered part of the official Metal Gear continuity, as the events of the game are incompatible with what occurs in the "official" sequel.
 * A sequel to the original Gradius (aka Nemesis) was made for the MSX titled Gradius 2 (aka Nemesis II) before the actual arcade sequel, Gradius II (aka Vulcan Venture), was even made.
 * Golden Axe II for the Sega Genesis was made a year before the proper arcade sequel (Golden Axe: Revenge of the Death Adder) was released.

Western Animation

 * The Secret of NIMH actually overtook the source material. While the Bluth film was rather jumping in and out of In Name Only, the ending (And primary events) of Bluth's 1982 Animated Adaptation pretty much ruined any potential chance of covering the two books written by Jane Leslie Conly with Jenner and Nicodemus kicking the bucket. (Whereas they both survived in the books; however it was implied that Jenner possibly died off-screen sometime in the first book with the mention of his party being electrocuted by a car battery). But Bluth honestly deserves this... his film was copyright 1982; Conly's books are dated 1986 and 1990, Chances are nobody even knew that Conly would take over or that the official book sequel would be released four years later. (Whether or not the supposed remake will follow the books more faithfully is unknown)
 * Bluth has also stated that if he were to make a sequel to Secret of NIMH, he'd actually cast Martin as the hero while Timothy was the villain. Interestingly, the sequel made 17 years later actually did the opposite.
 * He-Man and the Masters of the Universe: the series was put into production before the comic it was based on (and, by extent, the mini-comics that came with the action figures) could establish a concrete plot. This resulted in the story being retconned to fit in with the show.