As I understand it, S&W standardized on stainless circle inserts around 1973, but in typical fashion they used up whatever inventory was on hand. Prior to then, only stainless guns had stainless inserts. I recently looked at a 12-2 that dated to around 1975 and it had matching stocks with blued steel inserts. The Model 12's (into the 1980's) used unique grips that were different from standard K frame grips, so it's understandable.
Then again, I've been wrong before!
