Originally Posted by
seat1C
I think the previous reply's reference to a "single ticket" (from [MENTION=873105]Chiller3333[/MENTION]) is to a single ticket covering the two flights, not a ticket for a non-stop flight. If they interline luggage then they have a responsibility to get it from one flight to the other which increases their costs and potential liability issues if something goes wrong. They just aren't willing to do that if you don't pay for the service by buying an (almost inevitably) more expensive ticket covering both flights.
I am not familiar with the airlines cost-sharing agreements. But my thinking was going the other way.
If you fly A-B-C with BA on first leg and XX on 2nd leg, it is XX which is responsible for your missing luggage in C. The bag could have been mishandled by BA and never got to B. Hence, BA is discharging liability on XX for the whole trip. But I am probably wrong if there is a liability sharing agreement.