The U.S. DOT is NOT a joke. It has all the power that US citizens and legislators have allowed. In fact, Secretary Pete basically shamed the airlines into publishing compensation rules when they are at fault. He really had no official power to do so. So, shame on those of us who are American citizens for not standing up for consumer rights.

That said, I'm sure the airlines subscribe to some sort of centralized COVID database to keep track of the numerous rules. The agents are forced to abide by that database. Apparently, in the OP's case, it wasn't updated quickly enough. Since AA pointed it out in advance, wouldn't it have been easier to just get a booster -- or is that not easy in Canada?