Recently a friend and I were discussing the Harry Potter books and noticed that on Pottermore J.K.Rowling has occasionally contradicted the books. I'm almost certain that other Sci-Fi and Fantasy authors have contradicted themselves or their books in later interviews. I know if I was trying to remember every detail of a book I had written years before I would forget something so it is unsurprising that these authors do. My question is, if an author directly contradicts a book in a later interview which source do we use?
I would say you can use whatever you want, but it's really up to the community and the asker to determine whether or not they agree with your ordering of materials.
If the author contradicts the books, people are likely to toss it out. But if an author clarifies points not detailed in the book, we often accept that just fine (based on votes and checkmarks).
In some cases, such as with JK Rowling, there can be a disdain for Word of God answers, because some of the community feels that she seems to making new things up as she goes along, without regard to previously-established details.
A great answer would include an explanation of the original book/film/show (etc) source, and also explain that the author had later contradicted this. We're trying to educate and entertain people and help them understand things, not establish some sort of gospel for a one true answer.
In addition, it's up to the OP to decide whether or not the answer satisfies them enough to accept it. It's up to individual voters to decide whether they believe the answer is good enough to vote for, including whether or not any sourced information comes from appropriate sources.
An example of a (brief) 'good' answer:
Q: When Gandalf said "Use the Force, Harry!", what did he mean by "force"?
A: When Gandalf reaches the Undying Lands and meets Yoda, he learns how to combine his magic with midichorians. When he meets Harry, it's this mystical energy that he's referring to, so that he can defeat the sparkling vampires. However, in an interview in late 2020, Tolkien explained that he actually meant the F=MA type force, and that the midichorians never really existed.