Maybe that's where we went wrong. We didn't actually book a future cruise but made a deposit on a "Future Cruise Certificate" that offered "On Board Savings". There was nothing prohibiting combination in the Terms and Conditions of either the Certificate or the 4-cat upgrade promotion. I asked the Ambassador if they were combinable and was told they where (we were actually on a 4-cat upgrade cruise at the time). And, as I remember, Oceania had a very difficult time combining that 4-cat upgrade with a Future Cruise Credit from a previously cancelled cruise.