You can also ask Citi (via Chat, for example) for the account number. I recently opened a new Exec MC. My first statement closed and the miles didn’t post to the AA account. After a few days I reached out to Citi since I was concerned about them maybe having created a new AA account even though I had provided my existing number. The agent on chat gave me the AA number, and it was mine.

(I still don’t know why those miles and LP haven’t posted yet - it was in late Feb, so perhaps the special Feb processing had already started a bit early, but for 5 miles/LP I haven’t bothered to follow up yet)