Hmm that's a good one. I always assumed the 80-100k range as well before the training is completely shut down, but I didn't realise the fact that the training speed may very well reduce already around 50k.
If I check 21yo's on the list right now with a minimum of 50k salary there indeed is only one with 55k and all higher potentials are better trained.
I wonder if you have a larger sample for this one? Since the current 5 players won't say enough here and many U21 teams switched to higher potential players already.