I thought it was nearly impossible also, but then I started thinking...
From UBs match list, I get the idea that it's a primary care school. On the other hand, the avg step 1 score at Downstate is comparable to UBs (= national avg), and they place people in a lot of specialties at big name residencies, not to mention that clinicals at Downstate would be second to none. People might very well prefer Downstate over UB given both acceptances. People also might prefer NYMC for a preclinical education that yields a higher avg step 1, and might prefer stony brook for reputation, or clinicals.
And then there's location...a family member of mine went to UB (undergrad, though, not medical)...she said that a majority of the people there (north campus AND south campus) are from the long island/nyc area or just outside nyc (like westchester, rockland, dutchess counties). I think location would play a huge role for people accepted to UB and Downstate, stony brook, or NYMC. OOS students may also like the opportunity to do clinicals at these schools and live near NYC.
So yea, the attrition rate might be very high if a lot of people accepted to UB also got accepted to these schools, and probably others too.
And finally, I called a couple days ago to check on my status (still middle 1/3). I was told that its "safe to say" that there are "two-to-three hundred people" on the waitlist. He wouldn't go into any more detail. 👍