OK, well the thread referenced above about longhaul Basic / HBO fares probably applies then. The formal position is stated in the e-ticket, it should be clear there what is included in the fare price, including the checked baggage allowance. The confusion arises in that the oneworld airlines have launched this cheap(er) tickets, essentially based on no checked baggage, but different airlines have different policies about the specific details. The one that usually comes up here is that AA's equivalent fare - the same price as BA's fare on the same aircraft - does allow status passengers to a free bag on their metal, but not free advance seating. In fact you may well end up in the worst seats on the aircraft. BA, on the other hand, for the same fare allows seat selection on BA metal - including in some cases the best seats in the cabin - but absolutely zero checked baggage at all.

And this is probably what has happened here. Because it was BA metal, BA's rules apply. On Basic fares there is no checked baggage allowance for anyone at all on BA, and if you end up paying for checked luggage you should have bought the Economy Standard ticket instead, since that usually will be less cost overall. And if you think about it, on joint business ticketing it can't be anything else otherwise people paying the same fare, using Online Travel Agencies (for whom these tickets are especially marketed), they won't have a clue about BA, AY, AA plating, but could end up with radically different fees at check-in.

If the e-ticket says something else, please do revert, but the e-ticket is the contract for this aspect.