The tie-in novels are fanon, but they're a fanon that a) makes sense b) mostly agrees with what's on-screen in a harmonious way and c) is pretty universally accepted. I'd say this is one area where fanon should be respected unless there's an explicit canon contradiction.

I mean, it's not like most fanon where it's all about making Daniel a woobie so it's easier to pet him, for example (I'm looking at you, SG-1). There's actual depth there to the tie-in novels' Vulcan fanon.

(For those who don't know which novels are being referred to, here: Diane Duane's TOS novels, particularly Spock's World, Sarek by A.C. Crispin, the Vulcan Academy Murders and The IDIC Epidemic by Jean Lorrah, maybe a couple of others)