robbt,
S&W does not date their handcuffs like Peerless does by supplying them the serial number. I was told by Roy Jinks that the numbers on S&W handcuffs are not serial numbers like on S&W guns. He said any organization can have any series of numbers they wanted, applied to an order. With that said, I have not run across any S&W handcuffs with a duplicate number within any model I have collected.
You have what is referred to as a model 90. They started manufacturing these in 1952 and up to 1979 when they moved the handcuff manufacturing from Springfield, MA. to Houlton, Maine and started manufacturing the model 100.
When they started production in 1952 this was the first handcuff they manufactured, but it wasn't until 1958 that they assigned model numbers to their handcuffs, and these were known as the model 90's. Model numbers were not stamped on the handcuffs prior to the model 100.
So the models 90, 91, 94, 95, 925, 926, 936 & 938 did not have model numbers stamped on the cuffs, nor did the models 800 & 810 belly chains and 820 & 830 lead chains which used with the model 90 cuffs.
I have model 90's ranging from serial number 4388 to 195343.
I have a model 830 lead chain with a model 90 cuff with serial number 815209 on it.
Keys are a standard universal key that can be purchased from the factory or on eBay.
I hope this helps,
Dave