A few data points from today:
-KL 623 AMS-ATL 9:30AM was canceled yesterday so DL 75 (my 1PM flight today) went from J8 to J2 and Y8 to Y1 (the 10:35 AM DL 73 was zeroed out completely)
-Went to the ticketing desk at the end of Departures 2
-Was still able to do a Day of Departure upgrade from V fare.
-My ticket said class W from the prior complimentary C+ upgrade which I think confused the agent as she initially quoted me just 15K SkyMiles
-She then quoted me the correct 25K and 450€
-Then she noted that the flight was actually oversold and informed me the co-pay was waived and would only be taking the SkyMiles
I guess my question would be if I see something like this again, e.g. canceled prior flight and/or low (but not zero) inventory for sale should I just ask the ticketing/check-in/lounge agent if the flight is oversold? I don’t want to pay 450€ accidentally