Hoping not to bother anyone for a born on date, I looked at the Ultimate Highway Patrolman thread and found the SN ranges. I assumed that Smith probably made a steady stream of N-sized frames and, depending on the barrels and cylinders that went on those frames, they became 24s, 27s, 28s, 29s, and so on. Is this a safe guess? If so, my 29-2 was made in 1980. It matters for things like assembling the correct and expensive extras (!!!).
The s&w N frames are over 100 years old and go farther back to the pre model numbers, check there farther back. I think the 44 special maybe the oldest n frame.
OK, let me narrow this down. If I wanted to know when an N frame of late 70s to early 80s vintage was made, could I use the serial number range list from the ultimate highway patrolman thread to do it? Surely they didn't maintain parallel but different lists of SNs for all the various Ns made in a given period...?
As I understand it, nframes were produced and serialized prior to the specific caliber designation being made. So, basically, your assumption is correct!