I had a similar experience. AAdvantage Dining/iDine listed a local pizza place as taking Visa/MC, but I didn't make note of this at the time. I dined there and used my AmEx. When my miles didn't post for a month, I called AAdvantage Dining/iDine and said I had dined there and didn't receive credit. I faxed them my credit card statement since I couldn't find my actual receipts. They credited my account anyways. It wasn't until later that I noticed the pizza place accepted Visa/MC, but didn't mention AmEx.
Oops.
Steve