[Lynn Eades]

Sure the lenses can change,as well, but that's just about diffusion of light.
The placement of the filaments in (these "Pre- focussed" bulbs, we are talking about) dictates where the light is projected,(e.g.,on low beam, to the left or right) by the parabolic curve of the reflector, and hence the dipping left or right.

What I am asking Phill and Harry, Is, have the bulbs or bulb holders for left dipping and right dipping lights been mixed up, because the placement of the disc soldered on the bulb will be the difference between dip to left, or dip to right.

The lenses used to be the same, when the glass was a separate part from the reflector.
The introduction of the semi sealed and sealed beams, necessitated a specific LHD or RHD application. the bulb is a std bulb (same for lhd or rhd), but the bulb holder part of the assembly is rotated to hold the bulb at a different angle.
e.g. Std. American war time sealed beams are no good on Australian or New Zealand roads
Here are some other nearly relevant ramblings.
If you look at carriers for instance there was no adjustment at all for where the lights pointed.
With earlier cars, the person fitting the bulb had to adjust the position of the bulb, by moving it in or out of the holder, to get the best light pattern, from the reflector. This is why they came up with "Pre-focused" bulbs.