There is quite some give or tolerance in all these numbers. Let me say that the best way to get exact info is to get a letter from Smith for about $30 on your gun. That will give you the ship date, to where, the configuration as it left the factory and some other stuff. For those of us where rough time is OK: 1. Smith has routinely used left over parts to build transitional models, short run orders and what-not. 2. SNs are issued in order sometimes. They have been known to go back and use fill numbers not used many years ago. Groan! 3. Mod numbers (M19-3 etc.) have often been know to be mis-stamped. (I was so excited once when I called Mr. Jinks with a rare find and he said...shoot it. Nothing special.) 4. All the books and notes and sheets of info we have out here are cobbled together the best we can determine. 5. Getting the year right on your gun is pretty good. IMHO Enjoy.