We have no proof they should be used for lore. Either include all of them, or none of them.
He said they weren't in continuity, where as Frights says it's from the "uncharted corners of the canon" and Tales from The Pizzaplex says it's "set in the universe of the new games" either suggesting they're in continuity or just canon, just like TSE
Canon by Scotts definition is anything within the FNAF Universe. This includes the Original Novel Trilogy, which we wouldn't consider to be in continuity. These books may be canon, and help understand events in continuity, but unless we choose to accept the entire series as in continuity (Return to the Pit and all) then it should be treated as merrily canon, and separated just as the Novel Trilogy is.
We have no proof they should be used for lore. Either include all of them, or none of them.