Catering logistics doesn't really even *have to* get involved. Take catering out of the picture altogether, and then what you have is the FA with a list of pre-selections. Then the remaining pax can order based on the # of remaining meals. AA requires meal selection at least 24 hours in advance, which means anyone whose upgrade clears after that can't be on the list. I suppose there could be times when the # of preorders for choice A are more than provisioned for, and they could just (1) warn people up front when they order that it's not guaranteed, or (2) program the IT so that the meal options are tied into the catering provision, so if there won't be any steaks left then you're only offered one choice on the preorder.

Frankly, I'm not sure if AA even incorporates catering logistics and adjusts meals supplied based on the preorders. Obviously that's the best way, but they could still get it done without.