Originally Posted by
ThreeJulietTango
For premium cabin SDFC, only the original booking inventory is required. With upgrade inventories, that complicates things and probably glitches out their system. My interpretation is that C would be required and not E.
Upon further research, SDFC for mileage upgrades does require E availability, and then the upgrade must be processed again if available or waitlisted if not. The SDFC fee would apply.
I did SDFC twice last week on a confirmed SWU JFK-LHR flight. I was told the new flight needs to have 'C' inventory, else I can go back to coach and be waitlisted. Few hours before the flight, C space opened up and I was moved. Ticket number remained same.