If I want to upgrade with miles, does there have to be G/Z inventory available at the time of my request? My situation is that I have a flight next month SEA-ATL that I booked a K fare, but no G/Z inventory is available (although I think they may open some up in the next few days). I'd like to just have DL code in my request for mileage upgrade, much like a SWU is coded in. And then it would just sit on there until G is opened up. Is this possible? To be fair, I already called and asked DL, CSR told me it is not possible... but maybe if I play phone agent roulette I'll win? Anybody have any luck with this?