Are answers of the form "This didn't actually happen in the book (that movie is an adaptation of)" to a question "Why did X happen in the movie" acceptable?
Especially in cases where there seems to be no good movie-based answers?
Case in point: " How did Crabbe and Goyle get into the advanced N.E.W.T. class? "
The answer is: There's no explanation in the movie, and the book doesn't have them in the class so there's no canon reason.
Validity in this case is at the discretion of the asker I would argue.
If the flat fact is that "It didn't occur in the book, this is an oversight". While that may be factually correct in terms of the universe (books/movie/games/etc), doesn't mean this is the answer the person is seeking.
If what the asker desires is "In the movie universe, why did X happen" then those answering are being explicitly asked to remain in the terms of the movie.
TLDR: it varies for each case.
