Welcome from Virginia
Welcome from Virginia!
You probably will never find the date of manufacture because that would be the date that the pistol was assembled in the S&W factory. From there it would be test fired and then sent to storage to await an actual order from a dealer, distributor, customer, etc.
So the frame was stamped with a serial number at some date, probably along with a batch run of possibly hundred's of other N Frame revolvers, but then off to finishing, bluing, parts fitment, and finally...assembly.
The main reference book that we use is Standard Catalog of Smith & Wesson, which my 4th Edition, lists that N prefix serial numbers cover a multitude of N Frame revolvers (Model 25, 27, 28, 29, 57, 58, 520, & 629 (partial). Also SCSW shows 1980 starting with N700,000, and N800,000 is shown as 1980 to 1983 as Ron has depicted above. The only way to know your exact ship date (we use the ship date as "birth date") is to send for a Letter of Authenticity from SWHF. Instructions and Forms are on this Forum for obtaining a LOA should you want to know exactly when and where your gun shipped to, and exactly what configuration it had the day it left the factory. Very worthwhile in my opinion, especially since yours is evidencing unfired since factory test.
The thing with S&W is that they did not ship in any exact sequence of s/n dates. So even though a gun may carry a particular serial number...it may not have shipped until years later.
Below are some of my N-Frames that have all been Lettered and note that my 6" Nickle Model 27-2 is s/n N733XXX it shipped May 8, 1980, whereas my Model 29-2 is s/n N798908 and it shipped the very last day (New Years Eve) on December 31, 1980 per LOA.
As said...if you can snap some cell phone shots and post we will be able to assist you much closer with more info. Check the cylinder face at the barrel end...if it is COMPLETLY burn mark free...then someone has cleaned it, and it MAY have been shot. If there are only 3 burn marks (every other chamber) then it may truly be unfired since factory test.
Hang in there with us on this Forum...There are some real experts here on all things S&W so others will be chiming in with a lot better info than I, especially after you post some pics.