From what I understand, students with more than 1 ACCEPTANCE must choose which school they would like to attend by May 15. This allows schools to know how many places they still have open and need to fill up. If a student has a WL or is still waiting for the decision to be made from an interview than that does not count as an acceptance. Let us say you were accepted at school A & B, wait listed at C, and waiting for a decision at Einstein with a top interest in Einstein. By May 15 you would have to choose between A & B (lets say you chose A), giving up a free spot at B but you can still remain in contention at C and Einstein. On a later date (lets say June 1) due to completely filled spots C sends you a rejection but Einstein who finds your application spectacular accepts you because they still have space left. Now you choose Einstein and spot frees up at school A. Now your all set but that free spot at school A will be sent to someone still on the WL for school A. Now since students accepted after may 15 are usually given only 2 weeks to tell them if they will be attending or not most movement on the WL will happen in the next couple of days. Hope this helped.