I booked the following on one ticket from aa.com: (not really sure what you would call this type of ticket)

IST-LHR
BCN-LHR-DFW-AUS (on a separate day)

The IST-LHR and BCN-LHR legs don't show up as AA codeshares, rather BA flight #s. I'm AA Gold and purchased before the April 8 baggage changes. Upon check-out, the website showed that my free baggage allowance was 1 checked bag. I thought it possibly could have been 2 since I'm crossing IATA Areas on AA (LHR-DFW) and IST-LHR is within the same IATA Area. Though, I'm not really sure how the IST-LHR leg plays into it since it's about 2 weeks before the other part.

From what I read, the rule states: The MSC is, "for travel between two or more IATA Areas, the carrier performing carriage on the first sector that crosses from one area to another."

I was just hoping to clarify.