A very good point made by 747-436. If the union wanted the crew to position back on the same a/c they operated out on; that would have been fine on the first occasion because there would have been a crew in MEX to operate the return sector. How did the union think the next service would be crewed for the return sector as there would not have been a crew in Mexico?
Perhaps that is why BA rejected that idea, just a thought.
We are hearing two side of the story now.