SAMMI specs for +p came about in 1974. Any medium or small frame revolver made before that time should not use +p ammo. The exception would be large frame (Colt New Service, S&W N frame)as these could handle the more powerfull .38 "high speed", "high velocity", ".38/44" loads(all discontinued). 38spc +p is loaded to a lower pressure/velocity than the old high speed 38/44 load to be allowed in modern medium frame revolvers.
Not that I doubt your comments but did mfg's of these revolvers or pistols suddenly change their processes to strengthen their products after 1974?