+P in Model 64? Model 10?

[Gatofeo]

A man in YouTube left me a message, asking if he could fire +P .38 Special ammo in his Model 64.
The Model 64 is basically a stainless steel version of the Model 10.
Smith & Wesson 64 was first introduced in 1970 with a tapered barrel. In 1973, it began to be produced with a heavy barrel.
The SAAMI pressure limit for standard .38 Special ammo is 17,000 psi. The pressure limit for +P .38 Special ammo is 18,500 psi.
Without knowing when his revolver was manufactured, especially considering it could have been made prior to the introduction of +P ammo, I counseled him against firing +P in it.
Sure, the gun may hold up fine but it will surely strain it.
I advised him that if he must fire +P in it, limit its use and fire regular ammo for practice, reserving the +P ammo for self defense.

Myself, I have a nickel-plated Model 10 in .38 Special made in the early 1960s. It's nearly new and locks up tight, but I've avoided firing +P in it because I don't want to abuse it.

Did I give him bad advice? Am I wrong to assume that a .38 Special made 45 years ago probably shouldn't be fired with +P?
I know that some Colt and Smith & Wesson .38 snubnoses, especially those built on the smaller frames, are not rated for +P ammo. Am I wrong to be so conservative with a K-frame?

[John Traveler]

You may have errered on the side of caution.  No big problem.

S&W advises that any steel K frame revolver stamped with the model number in the crane cutout area (post 1958 production) is safe to fire using +P ammunition.  They still do not advise firing +P in alloy J or K framed revolvers.

The reason for advisising against firing +P in a pre-model stamped revolver is that at one time, S&W used a relatively mild grade of automotive quality steel in their barrel forgings.  The result was a ration of split forcing cones with the popularity of jacketed high-performance .38 Special ammunition since the middle 1960s.