The serial numbers don't have bugger all to do with production or manufacture years.
China to the best of the collective m14 world knowledge, has not manufactured new rifles since the early 90's
The serial numbers on rifles imported 2009 and newer denote export year. Previous to 09 , the serial number did not include import year.
Import year markings became a regular thing somewhere between 2005 and 2007 and were typically milled on right side of rear
Manufacture date and location can be determined more by the numbers that are under the stock line on lefy side of receiver. Not visible unless stock is removed.
Lee emerson , CGN member "different" is the guy to send the data to for production/manufacture year info