One would certainly think, no? I have faced this very scenario within the past year and, although it was UA that got me to DEN late ex-COS, I was confirmed into Y on the next available flight and placed on the "upgrade" list. The GA kept an eye on me and ultimately brought me a BP for F after I'd already been seated in Y. Very, very grateful for him but it never should have been so. My recollection is that particular ticket was around $11k, so I'm thinking not Z, but likely a mix of C/D. Insanity. Pure insanity.