There were two Chinese actually...one said he bought a PG who had like OD 14 and JR 5, and with first JR training it double popped (went from 5 to 7). The other one that you are talking about said they are used to train OD first on U21 players so JR gains an elastic effect from that.
I also received two JR pops in a row on a 21y old, 183 cm...but I don't know if it was from OD or any other guard skill because all of JS, OD, HA and DR were 8-9 levels above his JR. I also wouldn't train OD if I didn't train 1 on 1 first to get the elastic effect on OD, JR and PA, so I will never know if JR is affected by OD.