to determine the actual manufacturing date, you need to remove the stock and look for a proof mark on the bottom of the barrel just in front of the action. should be 2 letters side by side with a number underneath, either in a circle or with 2 swords splitting it up. the 2 letters designate the year of manufacture. I know for sure the following dates:
VB = 1970
DB = 1978
KB = 1984
but only up to 1984, after that I do not know the proper disignations.
my rifle has a DB on it for 1978 and a serial number R-77###