Absolutely Happened

"There was this one time, when I went to band camp..."

When something may or may not exist, but the series or its fans act like it definitely does.

The inverse of Fanon Discontinuity and Canon Discontinuity. See also Fiction Identity Postulate, Fanon.

Examples of Absolutely Happened include:

Anime and Manga

School Rumble only released the last three episodes of season three, but the rest happened. There's even a "previously on..." segment!
The first season of Kujibiki Unbalance did this too, except only completely random episodes were released.

Comic Books

Nextwave was planned to be in-continuity with the rest of the Marvel Universe then someone took their meds and realized just what Warren Ellis was writing and wisely placed it out-of-continuity. This has not stopped the Nextwave team members from remembering it and wearing their "uniform" in most subsequent appearances.

Film

The opening scene of Leonard Part 6 uses this trope to justify its title.

Literature

Daring Do, a popular series about the adventures of the world's foremost archeologist pony, has a surprisingly detailed trope page considering that some people claim it doesn't exist (except as a Show Within a Show on My Little Pony Friendship Is Magic).

Live-Action TV

While the episode "Black Market" of Battlestar Galactica is often treated as general Fanon Discontinuity, most fans tend to mix the difference: A black market exists in the Fleet. But nothing surrounding it involved an angsty Lee Adama.
An obscure puppet show called Candle Cove ran back in the '70s. Some people keep saying they see nothing but static, or that the puppets were mind-rapingly terrifying. Pretty silly things to say about a cute, if poorly done, pirate adventure story.
There's a hint in the script of Sherlock that while the title character is clean at the time of the show's setting, he has some sort of history of drug abuse. The fandom seems to have arrived at the consensus that the younger Sherlock was a mess, and at one point has overdosed to near-fatality - and that it was Mycroft Holmes who looked after him at this time. This is pretty reasonable, as old school Arthur Conan Doyle canon had him doing both cocaine and morphine, though he never seemed to (at least visibly) have a problem with addiction.
- Seemingly confirmed in "A Scandal in Belgravia", where after the supposed death of Irene Adler, both Mycroft and Watson take turns watching over Sherlock to stop him doing something stupid, making it appear very much like a suicide watch. As Mycroft makes a point of asking Watson if he's made sure he's checked his usual hiding spots, its heavily implied that they're preventing Sherlock from abusing drugs.
In The X-Files, fanon generally assumes that Diana Fowley is Mulder's ex-wife. This is never stated in canon and never fully explored. This assumption comes from the heavy implication that Diana Fowley and Mulder had a romantic relationship years before, and a scene from "Travelers" (set in 1990, during their partnership) shows Mulder wearing a wedding ring. No explanation is ever given for the wedding ring, leading to all sorts of fanon interpretation.
No definite answer has ever been given for the fates of Morgana and Guinevere's respective mothers on Merlin. Neither has ever been seen on-screen, and it's assumed that both are deceased. Nothing has yet popped up to contradict that theory.

Music

The general reaction to the Bob Dylan version of "Friday".

Web Comics

For a certain subset, Dr. Brinner: Ghost Psychiatrist.

Web Original

Inverted in Neopets, where Jelly World absolutely does not exist. That would just be silly (just to be clear, this is not discontinuity of any sort; denying its existence is only a Running Gag).

Western Animation

Cranking this trope Up to Eleven, 4chan members reminisce not only fave eps but the entire run of Saturday Morning Watchmen.
Invader Zim was canceled just when it was beginning to really develop its own Myth Arc, and with incomplete episodes in various stages of production. The creators have discussed many of their plans in interviews and commentary, and the audio recordings and scripts of several episodes were released on DVD and the Internet, and as a result most fans consider them canon. So, if you ever wonder why so many people refer to a past "Tallest Miyuki" or assume Membrane grew Dib in a lab, go look that up.
Justice League: Crisis on Two Earths was originally conceived as a bridge story set between Justice League and Justice League Unlimited explaining the changes between the two series, mainly the decision to expand the League past the initial seven heroes it started with. Though the final movie has a different art style and is meant to be in a new continuity on its own, all of the Continuity Nods to the DCAU remained. Many fans over look the differences and just accept it as the story bridge it was meant to be.
- There's a lot of attempts to put various DC animated works into the DCAU, and to connect certain ones to certain others.