You might also get a good answer from r/askliterarystudies

literally: a collection or list of sacred books accepted as genuine.

Anything written by either the original author, or by someone said author dictated as a legitimate contributor is canon by the definition of it being written by them. There is no requirement in the definition to determine whether the originating text is fully factual, and the very fact of temporal separation between writing and validation often preclude proof.