I'll also say that it depends on what the resorts occupancy is for any given time. If they have lots of empty rooms they can add more to the discounted pool. If a discounted reservation is cancelled and the hotel is at a high occupancy, it doesn't mean that discounted room goes back in to the discounted pool. It could be they will just let it sit undiscounted for last minute bookers who will pay more.
Personally if I am going, I book what I am prepared to be stuck with and pay for. If I find something discounted along the way, I book and cancel the other. But I always book what I will be happy with in the end.