One more thing is that there is some degree of tolerance variation on threaded holes.

I've come across more than one pair of older, BSA-threaded Campag crankarms which required a lot of torque in order to thread in a pair of Shimano pedals, even though the thread spec on both parts is the same.

I usually thread in the interfering part with a back-and-forth motion as needed to avoid exceeding a maximum level of hoop stress in the female threaded part. I've even used this method to force a BSA Shimano cartridge bb into a Swiss-threaded bb shell, with enough "loosening" back-and-forth cycles to allow a feel for the torque of the cups bottoming on the flange mating (right side) and the bb cartridge (left side).