A frustrating but tricky one. Even the sisters, BA and Iberia, have constant issues with their IT systems aligning and working together. Vast Legacy IT systems are not agile or dynamic so as good as the screens look to us it doesn’t mean the back ends look just as modern or organised, it at all.
I guess you can’t get a definitive answer because no one customer facing really knows unless you can access and sit with the BA IT team for a week or so to fully understand. Senor Cruz won’t have a clue why it’s so disjointed but that’s not his job. He’s probably posed that question internally himself.
I have definitely learned to book direct with BA. I understand it’s not always the case. But I don’t think BA systems likes Expedia or the others.
The different names is an interesting one and hopefully you can clarify that. Anyway I hope it gets resolved and you get your seat choice.