Originally Posted by
Quoren
Literally everything with the exception of stuff they clearly point out as being formulated by the opinions of outside authors, like From Lostbelt and Chaldea Case Files (though the setting details seem to be canon). But even then, Nasu could easily say that stuff is a parallel universe without issue. The absolute dumbest form of identifying canon is definitely the original author argument, like some people even seem to think other stuff sanctioned by the author isn't canon simply due to not being written by them.