Most Rats up until mid 2000's used CTS pots. To determine the date of your Rat find the 7 digit number on the back of the pots. The 1st three digits are the manufacturers code.
137 = CTS (Chicago Telephone Supply)
The 4th and 5th numbers are the year made (example: 1378509)
1985 would be the date for this pot.
(below) This is a pot from a very early "Fringe logo" Big BoxRat. Date code is 1979