I had my original number since 1986. Sometime in the mid-90s as I got older I ended up acquiring a new number. In 2010 I finally got around to dealing with AAdvantage CS and they found my old number and merged as it was clearly not an attempt to circumvent any rules.

Assuming you are doing it for non-nefarious reasons you can have them merge 2 AAdvantage accounts that are confirmed to be yours. Turns out my problem was my parents starting my 1986 account in my non-official govt photo ID name, so they never found it when we looked in the past.