This may not help in deciding upon a strategy, or maybe it does. Had a comparable recent situation. Had 1 SWU in my account, waitlisted with the SWU for C outbound from SFO, miles+copay for the return. Actually, the return cleared several days before the outbound leg. However, at the for the outbound departure, the upgrade did not clear, so 12+ hrs in E+. Several days later, upon checkin for the return asked the agent at ICN to now apply the SWU. But, noooo. It was not in my account, so paid the $$$ & had the miles deducted figuring that this would be easy to clear up. Not so, took about 6 weeks to get the SWU into the acount, then apply it to the return leg, then get a refund of the copay, and then finally get the miles returned. Moral, should have done copay outbound, SWU on the return. However, I think that day of flight is a factor. Outbound was on a Saturday, a notoriously bad day for upgrades ex SFO; the return was on a Wednesday where the conventional wisdom is that midweek upgrades from Asia are (relatively) easy to get. YMMV.