It seems that a lot of Harry Potter questions (including my last one) are answered based on tidbits of info that J.K. Rowling provided in various interviews.
I have two related questions (I'll post them separately):
Question #2 of 2. If there ever is a discrepancy between what JKR states in an interview, and a book, which one is considered canon? Book? JKR? Whatever is later?
(What made me think about this was the whole thing with George Lucas and his multiple layers of canon and the whole "L'État c'est moi" Luis-the-14th schtick he has).