They count their total grad student cohort as part of the whole psych department and accept a couple of grad students for each of the areas (cognitive, social and personality, developmental, etc.). Also, I think a couple of professors are taking their sabbatical next year.
Who are your POI's at Cornell? Just curious because I did my psych undergrad there and I work as an RA at Human Development now. Also, for those applying to Cornell's social psych program: My advisor who heads the program told me they only invited 5 interviewees and they're only thinking of accepting 1 or 2 :S