I lived in Raleigh for 12 years back in the 1980's and early 1990's, I'm very familiar with eastern NC as one job I had kept me on the road there much of the time. I grew up along the eastern foothills, though, and came back to them.
There's no definitive way to tell date of manufacture on older S&W's like ours. The SN range will get you within a year or so, but no guarantees because the guns weren't manufactured or sold in serial order. A letter from S&W Historical Foundation will tell the shipping date from the factory and who it was shipped to (dealer or wholesaler, but not the individual end-owner). A letter will also tell the original configuration of your gun, to determine if what you have has been modified over time (different barrel length, trigger/hammer type, finish, etc.) The Standard Catalog of S&W has SN ranges listed in an appendix along with years of manufacture for those ranges. Most people use those dates, along with posted numbers here on the forum from lettered guns, to get an approximate age. "N" serials start in 1969 and go through 1986, but the last several years was transitioning to a new system which started in 1980 with other models. Prior to the "N" range, the prefix was "S" which started in 1946.
The N400,000 SN range is 1977-78. N serial numbers are shared with many models; M25, 27, 28, 29, 57, 58, 520 and 629. So, chances could be that the SN immediately next to yours isn't a M27, but batch production would suggest there would be groups of models with consecutive SN's, although they'd be scattered all over the place when delivered. Your SN is early enough in the N400K range that it is most likely 1977, as is mine. Potentially, mine could be 1978. The SCSW is a great book on S&W firearms, if you like reading about that stuff. Right now, it's in the 4th Edition, published in 2016, but a new edition is in the works. BTW, a letter from SWHF is $100, worth the cost if you feel you have something rare or unusual. I only have one lettered gun, a M29-2 commemorative issue from 1979. I'm considering letters for a couple others in my collection, my M27-2 being one of them.
