My experiences have been good with missing mileage credit when calling in. After having filled out the aforementioned missing mileage credit form on AA.com and having mailed of copies of BPs/receipts for a YYC-ORD segment, they were able to credit the miles/segment when I called in about a month after I flew. In that case, that segment was showing as "J" class - same as a business class award, not eligible for miles.

Recently, I was involuntarily routed to CO for a MIA-TPA segment. I called in explained the situation and they credited me the miles, as if I had flown them on AA, within 48 hrs.