This is quite a common occurrence for destinations where no BA/OW option exists.

For example some small carribean islands etc.

But yes where no viable BA/OW option exists the BA website will price you and sell you a connection on on ticket on any airline they have an agreement for baggage with

You wouldn't earn tier points or haribos on the connection on AC etc, only on th BA flight, as I think they are selling you BA flight and then AC flight under the AC flight code.


cs