Worth clarifying as even AA don't always know. I requested a sticker upgrade by phone and the agent informed me I could not be listed as I had no stickers available (this was at least a month out). I informed her nicely that I didn't need to have stickers at the time of request and she went off to check. She came back and said "I never knew that" and put me on the list.
Perhaps most people request via aa.com but I was surprised.