I assume you refer to the technics SL-1200
Serial numbers for the 1200
Old-format serial number: NHOJF20765 (SL-1200 manufactured 1982)
The first digit shows the year when the SL-1200 was manufactured. These serial numbers contain no indication of the month of manufacture. It should be noted that serial numbers in this format contain no letters following digits.
New-format serial number: GE4FB001154 (SL-1200 manufactured June 2004)
The first digit shows the year when the SL-1200 was manufactured, while the month of manufacture is indicated by the letter following it. Months are coded as letters between A and L inclusive; A indicates January, B indicates February, and so on.
But i think you mean the models SL-1200MK2PE/PC and for more info about that history i think you should mail to panasonic. see http://www2.panasonic.com/consumer-electronics/support/