OK, the thought that old firearms made before the currently used steel alloys were available, and calibrated eyeballs for heat treat temperature determination were replaced by calibrated instruments are somehow capable of handling more pressure than more modern devices is ......not logical, to be polite.

The piezo electric pressure system and any data changes are the result of the more sophisticated and accurate pressure information available using the new systems (The copper crusher apparently wasn't capturing peak pressures in some cases). There's also the established fact that CUP and piezo electric PSI have no consistant realtionship. X CUP is not X PSI and no conversion factors exist.

For cartridges that had safe pressure levels established with the CUP system, ammunition proved to be safe under the old system is used to calibrate the piezo electric equipment. If X CUP produces a lower PSI reading, and that seems to be the case with pistol calibers, that's the new standard. If you look at the pressures for centerfire rifle cartridges, you'll notice that the allowable pressures seem to have gone up rather than down.

BTW, the powder manufacturers usually, but not always, do their load development/pressure testing in test barrels in a universal receiver with dead minimum chambers to provide themselves a worst case scenario for high pressures. Primer condition as a pressure measurement isn't all that accurate.