I don't know the numbers, but I do know that there is a good chance that a player will at least change his mind and possibly change it back before signing. People forget the guys that commit for 1 week, and they forget the guys that commit without a concrete offer, and they forget the guys that commit early but get dropped due to not having their grades in order.
There are any number of things that can happen in the last 8-10 months before signing day, and no one ever keeps everyone that commits in those first few months after the previous signing day.
And for that matter, it's no guarantee that the guys that do stay committed will actually make it to school, and then it's no guarantee that they ever see the playing field.
It's a lesson that took me about 2 years to learn, but recruiting, especially this early in the game, is pretty useless to follow. I find it much more valuable to wait and see who is contributing 2-3 years after signing. If you want to go back and rate recruiting classes based on how they actually contribute to their teams, then I'll care. Until then, who cares what some 4 star from Nowhere, LA says he wants to do?
Edited to add: I do realize that recruiting is one of the most important thing a coaching staff needs to be able to do well to have success, but as fans I don't think it's something we should try to follow too closely, because we really have no idea how well or poorly our team is doing. The coaches have a good idea if they did well or not. Other than them, everyone else is just speculating, and most are speculating without much to back up their thoughts.