A couple of weeks ago I wrote about the inexpensive flight where everyone could confirm an upgrade to business class for free.
Historically when American flies 3-cabin equipment domestically but sells the flights as 2-cabin (anything except for New York – Los Angeles/San Francisco and Miami – Los Angeles) elites and passengers on full fare tickets have been able to assign themselves seats in the business class cabin. That’s business class seating but economy service. Then upgrades are to international first class (with domestic first service).