The Examples of Fandom in Fanfiction
I found an interesting Reddit thread titled What is something people in your fandom forget isn't actually canon but fanon?. There are a lot of examples of the fandoms, that I can use in the introduction of my master thesis. These are the things, that are considered true in the fandom community, but were never expressed in canon or there was a conflicting information in the canon presented.
Some of the examples, that are could use are Hawkeye hiding in the vents or Avengers all hanging in the Avengers tower (MCU), that Snape is not godfather of the Draco (Harry Potter) or Akefia being the other Bakura's name (Yu-Gi-Oh) or that Kirk in the new movies had the allergic reaction after McCoy dosed him (Star Trek).
Another examples of fandom and ascended canon can also be found on the TvTropes and on Fanon entry on the fanlore.