That is a nice find. It's a 3913NL. No one is quite sure what the "NL" stands for, but it's a 3913 Lady Smith, but without the Lady Smith logo.
The SCSW says it was made from 1991-94. The SCSW also says that the VJA prefix was used in 1997.
The main differences between the 3913LS/NL and the regular 3913 are the angled dust cover, gray grips, and left side only safety/decocker lever.
Hold on to that holster. Holsters that fit the angled dust cover are pretty hard to find these day.
Also, take it apart, clean and lube it. Put some extra lube on the frame rails and get a new recoil spring. You want to protect the frame and rails from damage because S&W doesn't make them any more and doesn't have replacement frames.
If you want to find out when it was made, call the factory and give them the serial number. They'll at least give you the month and year, and maybe the exact date it was built.
Really nice guns. $400.00 is a very good price for that.