I would say ours has been about 50/50. We haven't WL'd that many times but we had some fill, others not. So many different variables. Room size, dates, views, etc.
We've only done one waitlist - but it was at the VGC for a 1-bedroom. It came through at around 33-days out. Whew!
It makes sense that the most likely waitlists to come through are shorter lengths at the bigger resorts. I would say BCV and VGF waitlists coming through are probably less frequent than say SSR or AKV. I think the earlier you waitlist probably makes a big difference too. We waitlisted right at 7-months.