So a pot stamped 1377833 is a CTS pot made in the 33rd week of 1978.
It seems quite clear however that the 125/126 was first introduced in 1954 and that their Club equivalents where born in 1957/58, when Selmer became the Hofner agent in the UK.
When it comes to the 127/128/Club60, information is more ambiguous.
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.
Stackpole and CTS made the pots in large runs also, so they may have shipped pots dated earlier than the year Electro-Harmonix ordered them. Some Triangle Muff pot codes are dated 1966, two years earlier than the founding of Electro-Harmonix!
Electro-Harmonix used pots from various makers, but they were usually the 24mm size, with 1/4" knob posts.
Logarithmic taper pots, or audio pots, will also work for the volume pot and sound better, but they are more expensive than linear.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.We also know that there where fairly long transition periods when old parts where mixed with newer parts.Therefor instruments manufactured during the same year can have different configurations in terms of pickups and controls.Year of introduction varies between 1954-1961, depending on source of information.