So a pot stamped 1377833 is a CTS pot made in the 33rd week of 1978.
Note that this does not mean a Muff with a 1978 pot was actually made in 1978, it just means it was not made much earlier than 1978.
In the second string of numbers, the first three numbers are a code identifying the manufacturer.
The next two numbers after the manufacturer number are the year, and the last two numbers are the week of the year the pots were made.
Electro-Harmonix used pots from various makers, but they were usually the 24mm size, with 1/4" knob posts.
The codes were created by the Electronic Industries Association (EIA) in 1920s to identify the product source and date of manufacture.
The first string of numbers is usually the part number, or sometimes the pot value.
Even buying new CTS pots today does not give you an accurate age because they are dated several months in advance of actual manufacture.The pots on the newer USA made E-H Muffs after 1999 do not have date codes.- All vintage USA Big Muffs have source-date codes stamped on the underside of the potentiometer cans, or “pots”.The pots are what the knobs are mounted to, essentally manually adjustable resisitors that control the voltage across a circuit.The Muff could have been made months or even years after the pots were purchased as it is known that Electro-Harmonix bought the pots in bulk, as did Fender, and other companies at the time.