You can't have 17 segments on a ticket, but there are ways around it. I've had several cases where schedule changes forced adding extra segments. Most recently, it happened before I flew the first segment. AA handled it by noting in the PNR, deleted a few segments from the middle (so it made a valid RTW and a ticket could be issued with no more than 16 segments) and then, after I flew the first couple of segments, AA added back the missing segments.

If you've already flown segments, then the extra ones can be added and a new ticket issued.

What complicates things in your situation is that AB didn't cancel the flight.