ALSO note: It is easy to confuse 5 digit and 6 digit serial numbers from this era, and hence get the wrong year for a guitar.
It should be clearly stated that Fender serial numbers ARE NOT definitively chronological. Basically there was a big bin of serial number plates, and the installers grabbed one, and screwed it to the guitar. The point is, don't read too much into Fender serial numbers.
Pre-1977 Fender guitars have a serial number on the bridgeplate or neckplate.
Fender Serial Numbers, 1950 to Present (Identifying the Year).
Serial numbers are basically chronological, but there is some overlap amoung years. As you can see from this over-simplified example, serial number assignment was fairly random. The only truely definitive way to date a pre-CBS fender is to look at all the dates on the instrument (body date, neck date, pot dates).
Fender serial numbers were assigned like this: bin with serialized plates/bridges. The serial number can only generalized the age of the instrument within a few years.