This must be my luck. Booked an (expensive!) one-way AMS-MUC-ATH, first segment operated by LH, seconds by A3. Both have A3 flight numbers.
So I booked through travelplanet24, (one of?) the largest OTAs in Greece. Turns out the ticket was issued on 050 stock (=Olympic)! None of the flight segments have anything to do with Olympic. Does anybody have any experience with upgrading such ticket? Will they deny since it needs to be A3 ticket stock? Guess I will call tomorrow..