i dont have any hard evidence to back this up, but I doubt schools would have filled their classes by January. There is sitll 3-4 more months left of interviewing at that point. I wouldnt be worried about interviewing for waitlist spots for at least another few months. But again, I could be way off on this one. Just my gut feeling tho.
It would depend on the school, but some purposely don't fill all their slots until later in the game just so they can potentially snag a few good late applicants without having to waitlist them. Even if you get waitlisted its not too bad. There's always waitlist movement so better to be on it than not.