Also here is an example, that the data we collect actually makes sense and is an indicator for how fast the player gains in training together with his market value.
We see here the 2 players from last seasons youth intake:

S 127 MC Youan-Bi 56.4% + 37.0%
and
S 127 ST Kouadio 59.3% + 32.6%

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It is clearly visible, that Youan-Bi is the faster trainer of both of these. He is lower rated, yet still has the higher market value compared to his teammate Kouadio.
Youan-Bi was projected to gain 37.0% if we had assigned a head coach to him, while Kouadio only would have gained 32.6%.
Of course Kouadio was the higher rated player to begin with, still the projected 32.6% were really low and similar numbers could be achieved by players who were almost 10% higher in their starting quality.

If we further collect data, we can pretty safely say who of your players will be worth keeping and who will not.