The following six digits are the unit identifier, although it should be noted that these final six numbers are not sequential and do not provide any other identification information about the instrument. S.-made Fender instruments, with exceptions including the American Vintage series and certain special-run instruments.
Indeed, we use these same books here at Fender when researching historical and date-related issues.
Serial numbers with an “S” prefix denote the 1970s (signifying a CBS attempt to use serial numbers to identify production years); an “E” prefix was introduced in 1979 to denote the 1980s. Vintage Series instruments and “V”-prefix serial numbers. “N”-prefix serial numbers denoting the 1990s were introduced in 1990.
As seen in the overlap of numbers and years, even these references to actual production dates are rather loose. The numbers and decals were produced far in advance, and some N9 decals (denoting 1999) were inadvertently affixed to some instruments in 1990.
Notice that there is quite a bit of overlap in numbers and years.
The only way to try to narrow the date range of your specific instrument is to remove the neck and check the butt end of the neck heel for a production date, which may be stamped or written there (if you’re uncomfortable doing this yourself, please refer to an experienced professional guitar tech in your area). Serial numbering didn’t change immediately because instruments continued to be made using existing, tooling, parts and serial number schemes.