What I meant was that, if I don't enter any FF number on the outbound segment, and then enter it before my return trip, will I only get half the miles and proportional MQD's? or would I get credited for the whole trip.

In the scenario that I only get half, I am pretty sure I will not cross into Diamond territory. This is what I want to do.

OTOH, if I enter my FF number on the way back, and they credit the whole trip, then I will cross into Diamond. This is what I don't want to do. Plz don't ask why