Showmebob, I think all of us wish SAAMI had tested and published equivalent loads using multiple methods, but if they did I'm not aware of it. It sounds like economics and policy, from my experience in corporations. No one wants to repeat a standard test because different results cause confusion. "What should we do? Issue a changed standard?" If it comes out the same, you've just wasted time and crushed another copper cylinder. Too bad, though.
Here's an interesting wiki on CUP:
https://en.wikipedia.org/wiki/Copper_units_of_pressure
They make an informative point, "Since a longer duration, lower pressure pulse can crush the cylinder as much as a shorter duration, higher pressure pulse, CUP and LUP pressures frequently register lower than actual peak pressures (as measured by a transducer) by up to 20%."
For those who visit that wiki site, note in the references at the bottom a nice paper reference written in 2002, "Correlating PSI and CUP," by Denton Bramwell. In it he finds CUP and PSI "correlated," but not "equivalent," with a good example for the difference being his increasing weight compared to his belt size - as one gets bigger so does the other, but it's hard to say by how much.
It's clear the use of piezo/strain gauges found higher peak pressures in common loads and so they dialed them back. Why they dialed them back, however, is conjecture, based on your social views, e.g., nasty lawyers, need to keep K-frames running, various conspiracies, real concern for customers, etc. I do note that Smith makes the 357 currently in J-, L-, and N-Frames, but not K, for what it's worth.
I do wish we had the earlier standard to compare, though.