Was the ticket ever reissued? I've seen folks here have problems where C (upgrade) space appeared to be available, including to the phone agents, but the agents were unable to actually push the upgrade through. However, I haven't personally seen where the upgrade was processed, and then reversed. If you had a reissued ticket in J, then my understanding is that AA needs to get you there in J (barring, of course, the carriers' blanket disclaimers in the COC where they take the rarely enforced position that all they are selling is transit A-B, and cabin is irrelevant.)