Zeerust Canon

A work is a sequel or prequel to a work that is out dated in one way or another but subsequent works have to keep them. Why? Because it's canon. One way of explaining this is that the work then becomes an Alternate History set in an Alternate Universe.

See also: Zeerust, The Great Politics Mess-Up, Cosmetically Advanced Prequel, Two Decades Behind. And Retcon, for when this trope is averted.

Anime and Manga

 * In Fist of the North Star, which was originally published in Weekly Shonen Jump during the 1980s, the war which destroyed the world took place in 199X and the term Seikimatsu ("End of the Century") is used to refer to the era the story takes place. Many spin-offs, remakes and video game adaptations have been produced in the years since the original manga ended way into the 21st century. The nuclear holocaust still took place in 199X in all of these spin-offs and Kenshiro still retains his title as the "Savior of Century's End".
 * Macross Zero. Macross, released in the early 1980s, had a unification war at the start of the 21st century. Comes the 21st century and Macross is still a franchise... let's use the war during the show anyway.
 * On an even more fundamental level, The Macross landed on Earth in the far off, distant year of 1999. The Earth was scoured with Zentradi fire in even further-off year of 2010.

Comic Books

 * Frank Miller's famous Batman work "The Dark Knight Returns" was written in 1986. The book deals with World War III, between the Americans and the Soviets. But according the book's chronology, it couldn't possibly take place less than 10 years after it was published (Comic Book Time notwithstanding) meaning 1996 at the very earliest. The sequel was released in 2001-2002 and features early 2000s technology and social commentary in the same way as the original had 1980s technology and social commentary. The kicker? It takes place only two years after the original! So not only did the Soviet Union live on into the 1990s and fight in World War III, but the world experienced 15 years' worth of technological advancement and political change in just two years! Not to mention that the events of the original series take place in 2009.

Film

 * Escape from New York, and its sequel Escape From L.A..
 * The Star Wars prequels are supposed to take place before the original films, which feature varying levels of Seventies and Eighties Zeerust. Lucas rather cleverly got around this by incorporating some elements of even older Raygun Gothic styles into the technology of the prequels; the uber-shiny ships on Naboo come to mind. This was to reflect the better overall quality of life in the Republic era; by Revenge of the Sith, much of the Used Future look from the original trilogy was back in place, representing the transition to Empire.
 * Star Trek uses Broad Strokes and an Alternate Timeline to try to walk the line between maintaining the look of the original series, including some very '60s elements like the female uniform of a miniskirt with go-go-boots, and making it look futuristic to a 2009 audience.
 * Interestingly, completely averted by the original film series, which made no attempt whatsoever to retain design elements from previous films or the TV series, if they thought they had a better visualisation.

Literature

 * Robert A. Heinlein wrote stories in a "Future History"; the first one came out in 1939. He ended up including typical sci-fi speculations such as moving pedestrian walkways by the 1960's and moon bases by 1999. Eventually this was shown in The Number of the Beast to be an alternate time line, where the list of presidents was "Roosevelt, Truman, Eisenhower, Kennedy, Kennedy, Kennedy, Kennedy, Kennedy, Kennedy".
 * The Number of the Beast also introduced a more elegant way to track parallel universes: apparently the person who first lands on the moon is always different. We live in the Armstrong universe; most of Heinlein's Future History takes place in the LeCroix universe.
 * Perry Rhodan, having started in the sixties, is a natural offender. When the material was cleaned up for re-publishing in book form, many elements were toned down (e.g. the Black and White Morality). However, on one book, the editor noted that he "just had to keep the pneumatic tube post, since it's a too silly idea to remove".

Live Action TV

 * Doctor Who and its Expanded Universe, which began way back in 1963, has a fair bit of Zeerust in its past but skirts round mention of failed predictions through its use of Broad Strokes continuity. Aside from the odd Mythology Gag.
 * As an example, the 1966 story "The Tenth Planet" was set in 1986, by which time the UN has an International Space Command with a base at the South Pole and Cybermen invade the Earth in a big way. (No prior story had taken place in the future so close in time to the present day.) The 1985 story "Attack of the Cybermen" managed to function as a sequel to this story without really delving into the way that Who history and real history diverged. The Backstory of the David Banks novel Iceberg, set in 2006 (though published in the 1990s), though, had the advanced tech and proactive UN as the logical follow-on from the "UNIT era" (whenever that was...)
 * The Doctor's now-former Robot Buddy K-9, first appeared in "The Invisible Enemy", which aired in 1977. Since then, at least in the parent show and The Sarah Jane Adventures, he has not undergone a redesign, so that his and in terms of his design aesthetic remains (at least in the parent show) remains unchanged. When K-9 re-appeared in "School Reunion" (2006), Present Day characters made note of his dated appearance.
 * The Star Trek prequel Enterprise took place before the original Star Trek. In the mirror universe episode, the Campy Zeerusty TOS era ship Defiant is sent "back" and everyone still marvels at how futuristic it is.
 * Star Trek also goes back and forth on this in regards to the Eugenics Wars. In the original series it was said to be a massive worldwide conflict that took place in the 1990s. Later this was Retconned (Latter admitted this as the result of a mistake on the part of writer Ronald D. Moore ) as having taken place in the 22nd century. However, canon nevertheless went back to the 1990s explanation eventually, with at least one semi-canon novel claiming the Wars were clandestine happenings underlying the publicly known events of the 1990s.
 * One episode of Voyager has them time travel back to 1990s California with no apparent war, though only a single war of the 20th century, one the US wasn't otherwise a party to, had a battle fought in the 48 contiguous US states and onscreen evidence suggests that the Eugenics Wars were fought largely in Asia. The same episode has a photo of the Botany Bay from "Space Seed" as a piece of set decoration.
 * Basically, the writers were gun-shy at openly proclaiming the Star Trek world as wholly divergent from the actual timeline of real history. They've eventually had to get over it, by default.

Video Games

 * The Metal Gear series is probably the kings of this trope, given its constant focus on the world of "tactical espionage".
 * The first Metal Gear came out in 1987 and takes place Twenty Minutes Into the Future in the year 1995 (or 1996, depending on the source), while Metal Gear 2: Solid Snake came out in 1990 and takes place in 1999. Both reference the Soviet Union and the StB (Czechoslovakian Secret Police) still being around, and one character in Metal Gear 2 (a Czechoslovakian woman named Natasha) compares her doomed romance with an American (Frank) with the Berlin Wall (which was destroyed the same year the game came out). The plot summary of Metal Gear 2 that was included in Metal Gear Solid attempted to retcon some of these details by claiming that the army Zanzibarland fought for their independence was not from the USSR, but from the CIS, and by making Natasha (who herself was later renamed "Gustava" in re-releases of the game) into a former StB agent.
 * Metal Gear Solid came out in 1998, but the game itself takes place in 2005 (six years after Metal Gear 2), and has such glaringly outdated things such as the use of the term "Japanimation" instead of anime.
 * Metal Gear Solid 2: Sons of Liberty came out in 2001 and took place in 2007 and 2009. The demo version that came with the original Zone of the Enders even had the Twin Towers in the background, which was almost kept in the final game until the unfortunate timing of the 9/11 attacks.
 * Metal Gear Solid 4: Guns of the Patriots came out in 2008 after the events of Metal Gear Solid, and the first half of Metal Gear Solid 2 had already passed. This also overlaps significantly with the Ruritanian Setting of the first two games, with fictional countries like Outer Heaven, and Zanzibarland.
 * Back to The Future runs into this with the 2011 Point and Click video game. The final episode includes both Xbox 360 headsets (from the Real Life 2000s) and the Mattel Hoverboard (from the second film's 2015).

Western Animation

 * Jetsons: The Movie takes place in the same canon as the 1960s series, but being released in 1990 has references to 1980's music and fashion.