Despite being 436s or 336s (with some odd cargo machines) the BA aircraft were all different and an experienced tech could tell which aircraft one was sitting in just by looking around the panels. I think Boeing made them up as they went along. The 747s tended to change as the line progressed as well, though you couldn't get down to individual tail munbers (except for Paddy Zulu) you could tell the batch by looking at the equipment fit.