Mamiya used a two-letter date code on components using a gold foil sticker. They changed these every few years so there is some overlap which will require a bit of guesswork to determine the components' likely era. I found the information below at https://mamiyarepair.com/mamiya-production-date-codes/
YEARS / LETTERS
1961-1970 / A-J (First Letter A = 1961, First Letter B = 1962, Etc. - Second Letter A = 1 (January) Second Letter B = 2 (February), Etc.)
1971-1980 / A-J
1981-2000 / A-T
2001-2014 / A-N
Finding the production Year and Month for my Universal Press was easy since the second letter was past 'J' in the alphabet indicating the 1981-2000 or 2001-2014 ranges. Since the production of this camera ended in 1991 the 1981-2000 range is confirmed. The code sticker applied to the body is 'BK'. The letter 'B' equates to 1982 and the second letter 'K' equates to 11 or November.
-Eric
