I recently purchased a 1983 Model 65-3 from the estate of a friend. It's a 3" with s/n beginning with ADH, which I guess puts it in 1983. Not counter-bored nor pinned.
It's beautifully polished, except for the top strap. My question is whether the polishing was done at the factory? Sadly, my friend is in no position to provide me with further information.
My knee-jerk opinion would be that the top strap was not polished in order to minimize glare while sighting the revolver. My EDC three inch 64-5 is polished with the exception of the top strap.
Your was polished after it left the factory. In fact in that time frame polishing a stainless gun would void the factory warranty as my brother in law found out the hard way.