fal308...I woulda thought like you but I found a -4 that was SOLD in 75. The -4 has different ser# format. Two digits before the K and only four digits after the K. Then to further confuse myself, just found record of having sold a -3, new in 69 that had no digits before the K903XXX.
Sam, I may be old but at least I confuse easily.
[This message has been edited by C.R.Sam (edited July 16, 2000).]
It looks like you are trying to make the S&W serial numbers track with change numbers. There is no correlation. Serial number patterns were usually changed when the numbers "rolled over". That had nothing to do with the change number like "-5".
I just have a pocket-size serial number, frame description and production engineering changes booklet so it is of necessity very brief. But according to it the K-frame had no prefix before the K (i.e.K 231255) up to 1970. In 1970 they started with 1Kxx after they produced K 999999. They progressed up thru single digit prefixes until 1977 when they went to 10K 0001. Sometime in 1981 they went to the three digit prefix. My booklet lists 91K 6801 - 124K 000. But it also states that in 10/82 they began the 3 letter prefix. Go figure.