Re: "This is the official Apple forum, and no administrator or support person has responded to me".
We are all Apple users, like yourself in this user-to-user community. Apple is not here, and very unlikely to even see your discussion thread.
Seems to me that American Airlines would be the one to check with.
American Airlines are the ones making the offer.
If your eligibility for the offer has expired, it's likely explained in their Terms and Conditions for the offer... eg: eligible only while in flight ? or maybe there's a certain length of time you that you remain eligible for the offer after your flight ? (ie: not the 2027 date when they stop making the offer available to flyers?)
If you haven't tried redeeming your offer from this webpage:
FYI: Found this Music log-in page from a link on American Airlines :
https://music.apple.com/us/curator/american-airlines/1436655442
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For letting Apple know: Here's the website for feedback, (incl. bug-reports, feature requests etc.): https://www.apple.com/feedback/
Note: Those who work behind-the-scenes are unlikely to reply, yet all feedback is carefully read and logged. Apple is more likely to act on a particular issue if many others send similar feedback.