I think nothing that doesn't make it on the air is canon. It would make great canon, but it's not? IDK Nothing J.K. Rowling says after the books is what really happened, to me. They kind of messed up the numbers with the whole Sam at Stanford thing, I guess, but they meant him to be just starting his Junior year, I think? I'm much more likely to accept changes to mistakes, but not anything deleted or discussed at a con.