You are saying that there are only three grades of players, right? So every player is either ST, FT or SFT. Therefore, every 18 y/o player may have one of three different Values (accordingly to his training grade).
Well, I don't see it. I see that Value can be anything in the given span, from certain number to another certain number (these numbers depend on the Overall quality). There are no steps in Value, it's continuous.
Of course, I may be wrong. I'm excited to hear your explanations on the subject that will prove your words.