I searched for a while and didn't find an answer to this, so sorry if someone points out that this has already been answered.

I am looking at a one-way mileage award ticket to Europe that involves an AA flight over the Atlantic, connecting to a BA flight. I'd like to use EXST to get three economy seats for two passengers. I'll call in and have an agent do the booking, but I wanted to ask if anyone had experience using this for a BA-operated flight on an AA award ticket. Thanks in advance for any info or experiences.