I guess back in the old days valves were joined to their bases by ladies who were paid on piecework rates. If the orientation of the pinch (the bit of the glass where the wires feed through) to the base didn’t matter then they would have put them together without paying much attention to it. In valves which were routinely run close to their power-handling edge, or were routinely oriented horizontally, then it did matter and they’d have to fit the base with the approved alignment. Once we get to button-base valves, where the electrodes are built up from a pre-prepared base, then there’s less room for manoeuvre.
VB