Yes it was a AA Issued Premium Economy ticket ... Upgrade was offered in the AA App / website ( can't remember which ) at checkin time ... receipt said "Upgrade (day of departure) " .. I guess similar may have been on offer at the airport

In the end I was connecting in LAX and my previous AA flight was delayed so I missed it .. but they rebooked me in J on the next BA flight so the upgrade was 'preserved'

So only tangentially relevant to the BA on the day upgrade prices, but $555 seems cheaper compared with reports of what BA has offered on West Coast - London .. prices above seem more like 2x that