The bus driver did register me, at least he compared closely my mobile "boarding pass" with his tablet.

And yes, I was eventually successful in retro-claiming the bus segments "flights" with BAEC.
The online claim was rejected without any comment, so I called them as to inquire what the reason for rejection was. They were not able to give / see any.
The lady from BAEC offered to open a new claim with the relevant details, it seems she was even able to find "XTZ" in her airport list.
Anyway, a few days later I got 10 points and a few miles credited (statement showed wrong booking class, which however did not make a difference in my case).