Thanks again for the help, everyone!
I called American and spoke with an agent just now. She put on hold to check, came back and said yes the "difference in taxes and fees" would be refunded. I assume there are notes associated with the PNR/ticket as she noted my wife was changed also without my saying so.
However, the instructions she gave me were to submit a request via the 'Share with us' generic link after flying. This isn't necessarily a confidence-inspiring process description. I suppose the way to do it is likely the 'Receipts and Refunds' link, but I wanted to see what your thoughts were on submitting after the fact or HUCA to try to do it now?