Pretty bad on catering’s part. No mainline equipment on AA has 12 F seats so don’t even understand how this happened.
Then again, I was on a DL transcon flight earlier this fall where they loaded the trays (with salad and dessert) for Premium Economy but forgot the entrees.
It could have been swapped for an A320 catering set, I guess? If it was just the mains, I've been on flights where the caterer left off one of the oven inserts (on UA) -- sometimes that will get you to 12 as well depending on the casserole dishes -- but it sounds like they didn't even have the trays to serve here.