I have a Model M Luxus and the serial number is all numbers as well. Just below the serial number and to the right there is the number 1079. The same number is stamped on the barrel near the receiver. When I had spoken to the gunsmith at the plant here in the US about adjusting the trigger, he informed me that the 1079 is the manufacturing date: October 1979. See if your rifle has a secondary number stamped below the serial number and/or on the barrel as that could be the month/year it was made.