I was on a paid business ticket in BA139 (LHR-BOM) on codeshare with AA few days ago. To my surprise at boarding the agent stopped me to let me know I've been upgraded to First! I was very surprised, I'm AA EXP, so OW Emerald but wouldn't have thought that this gives me any substantial priority as I fly BA metal max 2 times per year. Needless to say I accepted and was a happy customer.