Maybe being in the lawyer business will help - I find the rules maddeningly poorly worded and subject to interpretation (and you will find a zillion reports here of disagreements between wise and experienced FT members and various airline staff.)

Note also that OneWorld appears to be a very loose alliance, and each carrier seems to have great leeway in applying their own rules and charges. BA generally acts as if they're not being fairly compensated by xONEx fares and is relatively uncooperative in making tickets and seats available, while AA seems to be at the other end and is quite generous in many ways (except for their few "real" first-class seats in North America).