Opinion:
I only know on my on vehicle. The procedure is you push the vehicle back and forth while the nut is tight but not tight enough to keep if from sliding in and our and that centers everything. They you are supposed to tighten it to the specified torque.

The issue there is it is difficult to squeeze under the vehicle and most people don't have that size of wrench that would hook to a Torque Wrench and no room for a torque Wrench. In short I was able to reach with a Wrench and tighten it but not to the specified torque. (One of those procedures that if you had a pit to walk in under your Car would be best. Not sure if you put the Car on a lift if it would the drive shaft would center properly before you tighten the nut.)

If it was allowed to ride freely there would be no need to push the vehicle back and forth.

Also way back someone with an nut that wasn't tighten had worn out splines.

The Flex Discs are mostly rubber and their ability to flex should take care of expansion/elongation of the parts if they are setup properly to begin with.

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84 300D, 82 Volvo 244Gl Diesel