Failing to fill aircraft because some people would have to be upgraded is a definite way of NOT getting the best
PR! If there's seats in Club World or First, fill them! Upgrade Club passengers and Gold and Silver card holders to first and club as available, then upgrade lower grade Exec Club travellers through WT+ and Club and fill the plane.
BA has shot itself in the foot
PR wise with delaying people further.
But if they don't get catering back very soon, they'll be in even more do-do.