Originally Posted by
Changeup2000
From my recent rebooking experiences, it is quite interesting: I had a confirmed upgrade to business class. If I rebooked to AC codeshare flights, it only allowed me to rebook into economy cabin, but it allowed me to rebook into the business cabin on the partner airlines numbered flights, even though they were exactly the same flights.
That might be because on the codeshare, AC had exhausted its P quota.