First of all, training doesn't happen 3 times a week, it only happens on friday. Whatever the training you've selected prior to friday will be the skill that is to be trained on friday (trains players who've gained minutes at the training position, ofc).
Anyway, as far as I understand from your description, you're doing the right thing to get the maximum out of the training.
Well your player B got the training for outside defense, and yet he popped in JS and JR. Hmm did you, by any chance, change the training to JS prior to the friday's training??? but even then, that shouldn't be the case, because you played your player B at PG, so even if you accidently happened to select JS training for SG/SF, he shouldn't get any training for JS (unless he's also played as SG in other games, and from your explanation "I usually play Player B at SG when he is not training", I assume he also played as SG in other games, which gave him the minutes played as SG).
But anyway, if you actually trained Pressure (this can be checked on the Headlines, it will say something like "Ronald Tenorio reports that this week's training, which focused on "some skill", is complete."), your player B shouldn't get a pop in JS and JR. According to the training speed analysis, it doesn't say that training pressure trains JS and JR...
What about other players who you trained? did they get any pop in any skills?