I'd ask this over at the BA forum. This has come up before when another airline books BA, it sort of books on a fare that does not allow baggage. Which is weird because almost all fares allow checked bags, even award tickets. In coach, BA allows ONE piece of baggage from GVA to YVR via LHR.

The onus is with AC if they booked you but 'forgot' to put in baggage allowance. Or with UA as its their award ticket. Agents always assume that their computers will automatically add baggage allowance in but if they don't put an allowance on it, it will go to 0PC. It would have been simpler if they just reissued the ticket rather than communicate between BA and AC. BA will go with what it says on the ticket.