This was resolved today with a call to 1-866-419-0881, which was the number listed in the "Congratulations, you’ve been approved!" e-mail when I first got the US Airways Dividend Miles World MasterCard in March 2015.
The rep at the CC company called AA. This time, the AA rep made some effort and was able to find the info about recently expired miles. A few minutes later, the expired miles were credited to my AA account.
Too bad the AA reps on Friday were more insistent that I didn't know what I was talking about...rather than making a small amount of effort to verify whether what I was saying was correct.
Anyway, all is good now. Thanks for your help here!