I think you're mostly looking at B and C (which make up the majority of prospects) rated players development because they do not move ahead nearly as quick as A rated potential players. I noticed that depending on what kind of A potential the player is (A+,A,A-), he'll move up faster as well. I wouldn't worry about it man I think the system is a lot more variable then people think. I've seen players regress differently from different franchises, and this was pre-patch.