The SAAMI .38 Spl +P rating system came about in 1974.
At that time standard pressure was lowered, +P was increased very slightly over what used to be standard pressure, and Hi-Speed ammo was dropped from production.
Prior to 1974:
The Standard pressure 158 LRN grain factory load was rated at 855 FPS.
The 158 grain Hi-Speed load was rated at 1,090 FPS.
Under todays SAAMI standard, the same Standard pressure 158 grain load is rated at 755 FPS.
The +P is rated at 890 FPS.
As you can see, todays +P is hardly more likely to damage a modern gun then standard ammo was likely to damage it in 1970, or 1950.
And it is way less likely to damage it then those old .38 Spl Hi-Speed loads that were much closer to todays .357 Mag then todays .38 Spl, either standard, or +P.
rc