The plot of the movie follows a scoundrel named Dimitri trying to train a young woman ( known to the audience but not herself to be the real Anastasia) how to act like royalty and return her to her surviving grandmother for a reward. However, a persistent urban legend lived on that the youngest daughter, Grand Duchess Anastasia, somehow escaped, and several women came forward claiming to be Anastasia. Anastasia: Historically, the Imperial family of Tsarist Russia was executed in 1918 during the Russian Revolution.Disney eventually decided to go this route on purpose, throwing out their research and making the film into a "legend" rather than a true story. It was also problematic in that Smith claimed Pocahontas was only about 12 years old when they met. However, research into Smith's other works quickly reveals this to be bunk, because Smith had a habit of portraying himself as an entirely unrealistic demi-god of manliness and combat skill who found success, riches and sex wherever he went. This and most other works about Pocahontas are based on the writings of John Smith, which are commonly believed to be true. Pocahontas is a bit of a strange case.This lie inspired Millar to write Wanted and Old Man Logan. When wondering what happened to the heroes, his brother told him that they were all wiped out in a war with every supervillain. As a child, Mark Millar assumed that superhero comics were based on true stories.Reno Jones of the Gunhawks spends a few panels Retconning them out of existence.
Blaze of Glory has an In-Universe variant, with the dime novels based on the fictional gunfighters of the story, which look suspiciously like the covers of comic books published by Marvel Comics.Alan Moore has publicly acknowledged that he doesn't believe a single word of this particular theory, but it worked for the story he wanted to tell.
Played with regarding From Hell, which is based on one of the myriad theories behind the murders of Jack the Ripper - specifically, a variation on the theory that the murders were committed by a high-ranking member of Victorian society, on the orders of Queen Victoria herself, to prevent the victims from revealing the existence of an illegitimate heir to the throne.This may be a major source of "Common Knowledge" if it happened in a story that really took place, it must be true, right? And in works that are combinations of real events and fictional ones, it is all too easy to get confused about what actually happened and is possible in real life, and what is just artistic license. The net result of this trope is that viewers have to be wary of works that present themselves as a true story, as the creators may only be doing so because it makes people pay attention more. Best solution? Just say that it's fiction all along. The worst case scenario is when your supposedly true story is actually very close to someone else's actual true story, and you end up losing every penny of your profits in a humiliating lawsuit because nobody believes your sudden recantation.
A worse case scenario is that some folks get together and sue you for selling the story to them under false pretenses. The best case scenario is that you get a wry chuckle from your fans and a nod in a couple of papers. Everyone who visits the IMDb, for a start.