Another long time old gun crank trope is that everything has been lowered, watered down and weakened over the decades. There's a lot of truth to this, but there is even more outright fabrication as to why.
Since the industry has essentially remained silent about why, people make up what sounds reasonable, and in our litigation driven society today, "lawyers fault" sounds reasonable.
And, judging from observed results, not everything has been watered down. The 9mm Luger has been jacked UP!!!
The .357 Magnum is generally noticeably less than what we were shooting 40-50 years ago and that was a bit less than the original 1935 load levels.
Personally, I think this is so that the industry can sell J frame size .357s that don't get overstressed right away, that fired cases extract from, and that don't immediately damage shooters hands and nerves, but, that's just my opinion, and of course, worth what you paid for it.
I don't know when 43,500 CUP was changed to 40,000 CUP.
For the .44 Mag, I don't know, either. I do know that the Speer #11 (published 1987, my copy was bought in 90) listed 43,500 CUP as industry standard.
Speer #12, (published in 94) lists 36000 PSI as the industry standard.
I don't know if they are the same pressure, or not, and I no longer really care. Thanks to all the different measurement methods, and no handy consistent conversions between them, I no longer worry about what the actual numbers are. I'm back to the "seat of the pants reloading" where I go by the pressure signs on the cases and the way the gun behaves.
People constantly say how pressure signs are unreliable, and they are both right, and wrong about that.
Pressure signs are unreliable as indicators of what the amount of pressure is (the number of PSI, CUP, or what every system you use). Pressure signs won't and can't tell you if the load is 36000 or 43000.
What they DO reliably tell you is that you have pressure signs, and there for the pressure is excessive for your gun and combination of components, no matter what testing shows the number value to be.
Cratered primers, marks on the brass, sticky extraction, these things say "its not right" and that's what matters more than the calculated numerical value of the pressure in units.
Every gun and ammo/component combination can be different and handle the pressure differently. What matters most isn't what the book says, but what the gun and ammo in your hands does.
One time I ran some pretty warm 125gr JHP .357 stuff through several guns, and got different results. S&W M19, M28, and a Desert Eagle all with (nominal) 6" barrels. Velocities were 1620fps. 1670fps and 1720fps, respectively. Primers were flattened a bit in all guns, but the M19 required cases to be driven out of the cylinder with a rod, could not be ejected by hand. The M28 ejected by hand, and the DE cycled flawlessly.
Different guns, SAME load, different results. A different M19 might have given different results, cases might have ejected normally, I don't know, I do know that the individual gun we tested that day proved unsuitable with that ammo. Note I said "unsuitable" not "unsafe". There is a considerable difference.
So. take the industry pressure numbers under advisement, use them for guidelines. but pay the most attention to what the gun and ammo in your hands does. Even while being "book safe" not all loads are suitable for all guns, and different individual guns of even the same make and model CAN, when the stars line up the right way, give you unexpected results.