Not applying to Cornell, but a current Cornell psych undergrad. One of the current first year students got in off the waitlist, so it definitely is a real possibility not a formality. Keep your hopes up!!
Yeah I find it really confusing when programs do this. I definitely have not been notified of an official acceptance, but at the same time they bill it as a recruitment day (and the only other place which has done that for me is the place where I've been accepted). So I'll be going in assuming it's an interview but I do wish they were a bit more clear.
UCSB Social day was originally scheduled for the weekend of 2/5-2/7. A bunch of people couldn't make it then so they rescheduled it to 2/17. I do agree that generally social has been slow though - and it's extremely anxiety producing to not know if not hearing is a rejection or simply them not sending out decisions yet!
Sorry to be the bearer of bad news but I believe interview invites have gone out (or at least are going out right now). I received a phone call from a faculty member (though, interestingly not one of my 3 POI) this evening with an invite to an onsite interview the weekend of 2/21.