Is it possible to join duplicate threads? One of the threads will always become the more active one and ultimately the one that remains active. It seems a shame to lose the responses on the "losing" thread of the two.
I think it would work well, on thread 1 poster A (PA) responds a lot to OP but also to PB and PC, on thread 2, PX responds to PY and PZ. This happens on threads that where one to start with, too, so the joining wouldn't really interrupt the conversation much.