Here is an online application for decoding Fender Guitar serial numbers:
Guitar Dater Project
The Fender serial number decoder currently supports all documented MIA, MIJ and MIM formats with the exception of Custom Shop, Relic and Reissue instruments. Fender Squire guitars are also not supported at this time. Please note that fender serial numbers tend to overlap by at least a year, and thereby the date of your guitar can only be approximated.
It supports American / Mexican & Japanese Fender Guitars
Here is a second website with Fender serial number advice back to 1950
What other ways are there to date a Fender guitar? How can one be sure of the year a Fender guitar was built?
Do people as a rule try and validate the year of manufacturer before paying big bucks for one of the vintage instruments?