UMMS does not admit more than the class size. The school cannot accept more than 125, as there is only enough funding for 125 students per class (your tuition is subsidized by the Commonwealth, yada-yada). This is a major reason why the cycle here is so long. I'm not sure how many people come off the waitlist, but it is a large number. Bear in mind that the wait list here is a bit different in that this school doesn't overaccept, so your chances of getting in are still decent even if you're on the waitlist
For anyone wondering about the quality of education we have here, last year's median Step 1 score for UMMS was 236 (national was 228). With the exception of a couple years, we have consistently scored above the national average over the past 10 years. Plus, we're a true P/F school (no ranking for the preclinical years).