Don't know if you saw this already but it might have something to do with it:-
From the 8.02 changelist
- Ensured scout's with high judging potential aren't as accurate when rating players for potential.
Plus I've noticed aswell that the initial report isn't always accurate as apparently the staff reporting on them to need to see them in action as it were. So I'll often have a coach say a player's potential is at one end of the scale, then 5 or 6 months later that can change which I'm guessing is a simulation of the staff member seeing the player concerned in training day in day out, plus performance in matches (U18/Reserves/First Team whichever is relevant).
Rather than getting a coach report right after they sign, maybe wait a few months so the coach can see him in action. Just a suggestion