I appreciate the above links but that website, for M14 use, unfortunately is not reliable. I have known about the problem for a long time. If you enter a serial number like 845192 in Winchester's search, it comes up the rifle was produced in 1962-63. The only problem is that serial number is an H&R. It should exclude that serial number, but as many different contracts were running at the same time, it OKs anything searched between the very first rifle and the very last rifle of that contractor, even other contractors' serial numbers that fall between those two.
The search can determine only the approx time period. The results are not programed as to which manufacture the serial number applies to.