i was going SAN-SLC-OAK in Y with confirmed V on both segments. But when I checked in at SAN the SLC-OAK leg had been canceled. So the agent said he could try UA if I preferred SFO. I said okay, but he responded that there were no more F seats open on the SAN-SFO flight. So I rerouted on DL on a SLC-SJC flight, booked into F.

i'm always curious about DL's policy on upgrades and schedule changes. i had a similar experience going BHM-ATL-CMH when the BHM flight got in after CMH's departure. Confirmed V on both originals and I was allowed to switch to DAY and was given F. but their terms specifically say DL is not required to give F/V/X if there's a hiccup. No complaints clearly, just glad i've gotten above and beyond customer service reps!