I have emerald status. Qatar can assign the seats if the flight is designated a Qatar flight. They can not assign the seats if it is sold as an AA code share. Neither can AA. So, if you get it as a code share, 72 hours is the magic moment.

The 72 hour call worked both on our outbound and return trips. It will get riskier I suppose as the planes fill up

By the way, both AA and Qatar acknowledged that this was a "computer" (aka software) limitation with the relatively new code share arrangement. Neither had any idea when it might be fixed though.

My thought as I have additional flights like this coming up: keep checking back periodically to see if they can assign the seat prior to 72 hours