Originally Posted by
xliioper
No Medallion window C+ (or FC) upgrades on VS coded, DL flights. Like FC, C+ cabin is a separate fare class on DL (and not just an extra legroom coach seat) and the system can't process you into the DL SU comp upgrade C+ class as VS does not have an equivalent class (domestic FC upgrades likewise uses separate OU class). You may be able to get access to C+ seat on day of departure, but most likely it won't be anything decent.
I've only flown VS ticketed/DL metal award flights domestically, but they've all been DL marketed and I've received upgrades at the usual GM window.