S&W started model marking firearms in 1958.
However, non-model marked guns could possibly be shipped later than that (although an extremely uncommon find), as S&W never threw anything out- at least, that is the consensus.
However, a straight model marking, for instance, "Model 14" does not necessarily mean that it was the first of a model- it means that it was the first of that type to be model marked.
The "Model 14," for instance, was called the K-38 Target model before it was named the "Model 14."
The worst misuse of nomenclature is when someone incorrectly calls a model a "Pre-14." There is no such thing as a "Pre" model number anything. It would be correct to call it a "Pre-model marked" or in the case of a Model 10 that was made between 1945 and 1958 and isn't marked, simply, a
Post-war M&P.
The "Pre model" gets my dander up, but I really have no reason to complain, as I make enough...I mean plenty...ok...too many mistakes on my own.
It just puts me in mind of this fellow:
I, as well as many others here would highly recommend adding this to your collection and bookshelf- it will explain all...make that most.