Originally Posted by Blumie

It's entirely possible that they treated you as an "involuntary reroute" and reacommodated you in Z, at no cost to you, but it's impossible to know based on what you've told us. I wouldn't do anything at this point other than monitor your account to see if additional miles are deducted. If this were going to happen (and I don't expect it to), I would expect to to happen fairly quickly. I also wouldn't expect there to be any problem with your reservation going forward, but again monitor it on aa.com regularly.