Marlin Original Goose Gun, Date of Manufacture? 55

I have one of the "the original Marlin Goose Gun" model no 55. I would like to know the date of Manufacturer. I have read it is part of the letter code in the serial number but this one has only numbers, no letters.

The serial number in part is 713***34. Can anyone date this long bbl shotgun. I cant find a good answer on Google or Ask. The only correlation is the last number 4 meaning 1996 as date of MFG. Help me please!

Thanks Marlon