What I am talking about is walk on players that pay their own way and then eventually get a scholarship - or leave to take a scholarship somewhere else that they could have taken straight out of high school.
EDIT: Your method of uncovering those players is invalid -- because they are not people that are enrolling in the middle of a year. They are already students at the school from day one and are on the team as walk-ons originally.
You may or may not be able to detect them by checking for changes in the names of players that have scholarships by class over time and/or by the number of players that originally were in a class versus the end -- but they still had 85 scholarships. It isn't trivial to unwind -- and it is perfectly legal (so not saying Saban is breaking any rules, just taking advantage of Bama being cheaper than most private grade schools).