Originally Posted by
DCADeltaRoadWarrior
You can SDC when you have a PAID premium cabin seat to another flight, if there is availability.
That doesn't apply to RUC's or complimentary upgrades that have already cleared.
There is a big difference between an upgrade instrument (RUC/Miles etc) and a medallion upgrade. The medallion upgrade can only SDC based on the original coach bucket. With a RUC it is treated as a first class paid ticket. The upgrade instrument is the method of payment, just like if you had a first class award ticket you can SDC to another seat.