"I understand how the training letter works." Obviously not. The last class of new hires, from April, is still in training. Their class has just been cleared from the training letter. Guys whose classes have already started drop off the training letters all the time, on all the various airframes.

As for no training til July, as the 727 is a pretty low priority nowadays, (almost as many reserve lines as regular lines,) they aren't in a rush to train new front seaters. As for second officers, none of the upcoming classes is going to the backseat, so no SO training unless a guy turning 65 wants to stay. Doesn't seem like a big mystery to me.