I agree that make’s good common sense. It would be interesting and infomitive to know the source and exact wording. All though law’s and regulations do not always make common sense! We could also argue the intent and or interpretation of said law or regulation that we have not seen yet.
Because of acceptable variances some thread’s are better or closer to optimum tolerance. I can scwew my regs and fittings into the valve but at the dive shop it is too tight to attatch there pressure gauge. Making it very easy for someone else unintentionally cross threading a good but not perfect thread. Brand new valves pass acceptable specifications but could be better!