So, the original art of manual loadsheets, manual check-in, cabin crew actually physically counting SLF on board has died.
I do recall, not so many moons ago, actually practicing this exact scenario, not for BA fortunately, but another EGLL carrier. Yes, minor delays, some inconvenience but an effective proof the pencil and paper still has a very prominent place in today's modern technological era.
Me, always one never to rely solely on IT, especially outsourced and someone who I cant shout at if it goes wrong.....