Let's not let the potential for errors deter us. Basically the only things we have to worry about are distances and angles. If we design-in the ability to affect these things, it's not that daunting.

A note about Bermpohls; since they use glass mirrors, refraction errors are introduced when the light strikes these at angles. You'll notice that two of light paths have slanted glass in front of the film-holders to correct for this. Pellicles though, are so thin that they don't introduce any appreciable error.