"Dose the pin date the gun?"
Yes, it does.
S&W dropped the pins (and the recessed chambers on the centerfire magnum revolvers) around 1983.
In some models it happened earlier, in others later. Some revolvers also show one feature and not the other. They're called, roughly, transitional models.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.