Ok thank you all, that helped a lot.
So, to summarize, if I had a player with 10+ JS, HN and DV and 2 JR I may train him in outside shooting even for an entire season without ever seeing a slow down in training intensity? Well, actually JS, HN and DV are all secondary skills improved by Outside Shooting and they might be slower than usual to pop, but the primary skill for this training, JR, would be fine, right?