(If you are not comfortable performing this operation, please use an experienced professional guitar tech in your area).
The serial numbers do not immediately reflect the change, as CBS continued to make instruments using existing, tooling, parts, and serial number schemes.
While there have been periods where dramatic changes have occurred, for example: the transition periods between Leo's Fender and the CBS years, as well as the transition between CBS' Fender and the current ownership, generally speaking, most models are feature specific and do not change from year to year..
Serial numbers have been used in various locations on Fender instruments through the years.
It should say “quality assurance” on it and have someone’s handwritten initials and a 2-letter code on the bottom line.
The first letter indicates the year it was made, the second letter the month.
The following chart details the Fender serial number schemes used from 1965 to 1976.
You will notice that there is quite a bit of overlap of both numbers and years.
Inside your amp’s cabinet is a little sticker, usually to the right of the speaker.
As an example, if your amp says “JB,” then it was made in February of 1999.
Information on Japanese and Mexican-made instruments is included towards the bottom.
They have been placed at the top of the neck plate, on the front of the headstock, on the back of the headstock, and on the back of the neck near where the neck bolts onto the body.
They were stamped on the back vibrato cover plate (early '50s Strats), and on the bridge plate between the pickup and the saddles on some Telecasters.