I don't know how many they put on the wait list, but they put them in an order, and as a spot opens up, Kaye will go in order down the list and offer the spot to te next person waiting. So if they went through 120 alternates before they filled up their 40 person OOS, then that gives us pretty good odds!
I've heard at least that they accept 70 originally for those 40 spots knowing some leave- then go to the wait list for potentially 71-120? I think they wait list up to #250 but that could have changed since I last heard.