Here is my model 13-1. It is the subject of my post in S & W. Revolvers, 1961 to 1980, "Model 13 anomaly?". It was bought new in 1974 or early 1975. It's s/n is 3D15XXX. Model 13-1 was made from 1974 to 1977. There are 2D prefixes listed as produced in 1977 and 1978. 4D starts in 1979.
There are no 3D prefix serial numbers listed. Maybe it jest don't exist. I
requested a letter on it a while back and will add info to the post when I get it.
teesur.