Am I understanding you right that your saying the pinion bearing preload is not solely determined by the pinion bearing spacer, that if you set up the pinion preload then change the pinion depth it changes pinion bearing preload? I see the point of setting the preload last so you can tighten down the pinion nut to achieve drag for checking the pattern. And it's necessary when your using a crush sleeve since you usually have to take things back apart a couple times to get the pin depth right.
As I was writing this it just occurred to me that if you add a spacer behind the rear bearing cup that would change the pinion bearing preload since your changing the distance between the pin bearings. From my experience, which I'm sure isn't anywhere near yours, if the pinion bearing preload is set up and you add a shim between the rear bearing and pinion gear it doesn't change preload because you never changed the distance between the bearings.
