Double stamped serial number plates were also produced (number on both front and back of the neck plate) in late 1957 to early 1959.
Unfortunately, there is also some overlap in serial numbers between years — again due to the fact that neckplates were re-ordered various times from various manufacturers.
So, without any factories FMIC moved all guitar production during 1985 and early 1986 to Japan, while FMIC built a new factory in Corona, California.
The serial number can only generalized the age of the instrument within a few years.
In mid-1954 Fender changed the location of serial numbers to the neckplate. Because different companies did the stamping of the serial numbers on neckplates they vary in location and layout.
In 1957/1958 some serial numbers started with a minus sign (“-“), or had a “0” prefix before the number.
Also in 1959/1960 some serial numbers were at the bottom of the neck plate instead of the usual top.
This time, probably in a corporate branding effort, a large Fender script “F” was added to the neckplate below the serial number.