Hi Steve, you got it. It's easy for the early Plombs. Like Snap-on, Plomb put year dates up to 1941. Actually, I found some early 1942 sockets with a number stamp. But, most of the war years had letters stamped on them. TWERSTY did the research and found that the letters coincided with the years, B=1942, C=1943, and so on. For the 1/4 sets, 1944 and 1945 rarely had markings, but the designs are giveaways. Also, the square edge Plomb boxes during the war had some nasty, ugly, sticky paint that will probably never die. Then came the round edge boxes. After the end of the war, the tools were chrome again and the tool boxes were coated with red paint and new logos. During the transition to Proto, the tool design remained consistent with the last Plomb sets. Moving on to early Proto, the Flying Lady was painted on all the Proto boxes. They also remained the same design from the Plomb years.