BA staff in the check-in area were outstanding when I ended up in SEA last December, after AC rebooked me on DL but failed to ticket - and then the rebooked DL space was gone.
Not all the check-in staff were trained on ticketing, but one was extremely helpful, held the space, and spent 30 minutes with Air Canada ticketing on the phone getting me sorted as the cut-off got closer. She got a Golden Ticket and a ba.com/welldone sent her way...
Were you trying to ticket at the check-in desk or lounge?