If you are ever lucky enough to come into possession of some old Craftool stamps, it is nice to be able to determine when they were actually made.
Stephan Szeker gave me this concise summary:
1. CRAFTOOL CO - No Number: Most likely made before Craftool started putting the numbers on the tools circa 1950.
2. CRAFTOOL CO. - Only a number: It was made prior to 1963.
3. CRAFTOOL CO. - With a letter prefix & number: It was made between 1963 and 1968.
4. CRAFTOOL CO. USA - With a letter and number: It was made after 1969.
5. CRAFTOOL USA - with a letter and number: It was made more recently.
6. CRAFTOOL - with a letter, number and "S": ???
7. Craftool Pro - with a letter and four digit number: A special edition available from ???? to 2018.
From other sources I got a few other facts:
Craftools have been made since the late 1940's.
With such a long history, even stamps with the same number actually can have very different impressions, depending on when they were made.
In the early years most tools were hand ground by a master craftsman. Later on, tools were formed by die stamping on a machine and show no evidence of hand grinding.
Craftool Co was bought out by Tandy in the early sixties.
As each different Craftool era arrived, new tools were introduced and some were dropped from the line-up.
This is from a 1949 Tandy Catalog:
I will continue to add to this post as I get more information.