Some interesting info from factory letters;

The first production Model 629 had serial numbers that began N 629xxx these were basically test guns and guns for the writers. Although we shipped some of them to distributors such as Bill Orr’s company GT Dist. The first lot of 350 units were serial numbered from N748564-N748913. These were the first group produced for sales.
Production started at N748564 in 1979 with the 6” guns! The 4” and 8 3/8” were introduced in 1981. The –1 guns started in 1982 and approx at this time they changed to the Alpha-numeric serial numbering system.
jcelect