Per AAMC rules, by March 15 schools have to offer at least as many acceptances as there are spots in their first year class. So for UIC, they have to give out 180 (Chicago) + 60 (Rockford) + 60 (Peoria) =300 acceptances by March 15. They don't have to finalize the class by this point, only send out the acceptances.
And yes, the lack of transparency makes it harder for UIC to know who they should send acceptances to because they don't know where else people got in. For example, if they were reviewing an app and could see the person already got in at Northwestern, UChicago, Harvard, etc., odds are good that person would end up choosing one of those other schools and it probably wouldn't even be worth it to offer them a spot. Likewise, if a person holds no other acceptances, UIC could be pretty sure that person would take the spot if offered and might wait until the end of the cycle when they need to fill the class to actually send out the acceptance to that person. Remember, schools are trying to fill the class with who they feel are the best possible applicants. Since they can no longer see other acceptances, this "will they/won't they attend" game has become much more ambiguous for adcoms.
This doesn't necessarily help those of us who are stuck here in the middle trying to chase our dream of med school, but that's the game and it's the life we chose.
