Assume a college has 1000 places and it accepts 1500 students taking its yield percentage into consideration. What happens if ,say, 1200 students accept the offer? What will the college do then?
The college will deal with it. It happens virtually every year at some colleges, although not to that degree. They biggest issue is usually housing so they turn singles into doubles, doubles into triples, common areas and study rooms become dorm rooms, dorm renovations are postponed, etc. They might also encourage students to take a gap year or defer matriculation until second semester when student populations usually drop slightly (semesters abroad and early graduations).
I forget which school this was, but when I was touring campuses last spring, one college said during their info session that they actually accepted too many people one year and had some of the freshmen stay in a nearby hotel for at least a semester. So maybe they would also implement a situation like that?
Colleges have ways to handle it if they under-estimate their yield. Some will offer spring admission, others will open up more dorms, encourage more upperclassmen to live on campus, etc.