Wouldn't Star Wars be like this as well? There's a pile and a half of books for SW that are all supposedly "official" as well. Plus those animated shorts that happened between two of the prequels.

Though I guess it would be harder to say since Star Wars isn't an ongoing thing, so there can't be any "new" and "definitely official" stuff that could possibly refer back to any "fan" stuff to bump it up to "possibly official"