So I haven't encountered this situation before, but say I have a SWU "Valid through Jan 31, 2019".
Now let's say I find a flight which departs on 1/31/2019 where there's C availability all the way, but some of the segments leave 2/1/2019 (in particular, the long haul segment). Say, SFO-MIA(redeye, 1/31) - GRU (2/1).
Will the SWU expiring 1/31 pull for this one if I clear right away?
Does it change if I get waitlisted on the MIA-GRU segment?