Originally Posted by
MSPeconomist
Just make sure that any C+ upgrade doesn't consume a RUC. On certain international flights, it can easily happen: apply a GUC and C+ is available, then if D1 upgrades open up later, DL will ask for a second GUC. This is supposedly the new DL policy, especially as premium economy cabins are introduced as not only a separate fare class (W, WP, etc.) but also a separate cabin class.
RUC does not upgrade to C+ The policy you're thinking of involves GUC and upgrades to PS/D1. If you apply one to get PS then want to goto D1 it requires another GUC. Nothing has changed in regards to RUC/C+, which C+ isn't even on planes that will have PS.