Originally Posted by
Pianoman109876
you technically didn’t “upgrade”- you paid a fare difference and had the ticket reissued (hence the revenue fare-class of “C”, not “OU”). COMPLIMENTARY upgrades ARE lost.
Also, AFAIK so are the upgrades where you pay to upgrade your seat on a segment. Those are supposedly nonrefundable too, although DL agents have been known to make exceptions.
OP is lucky that the purchased upgrade was the sort that involved upfaring to a FC ticket (which also allowed an easy SDC into any open FC seat with no fare class availability requirement).