I didn't apply to Nova, but I'll throw you a bone here anyways. I think that most schools will rank their waitlist, and as seats open up, naturally they take from the top of that waitlist. However, they may not initially rank past the first 10 or 15 unless more than 10/15 seats open up, then they will further rank the waitlist. If a rank was not stated in your waitlist letter, then it's possible you are not in the top 10/15. You may want to call and ask how Nova does things.