There were periods of time when this was not consistently done, (between 19), and there are certainly other examples of short periods of time, and individual pieces, where the dating was simply omitted.
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.
But once again, due to the modular nature of Fender's production methods, and the fact that most serial numbers schemes are not sequential and usually overlap from between 2 to 4 years, (from the early days of Fender, through to the mid 1980s), dating by the serial number is not an exact science.
So, obviously a neck date, while being helpful in providing a date range of production, it cannot be a definitive reference.
Unlike the auto industry which has specific model years for their products, most specifications for a given Fender instrument model, change little if any, through the lifetime of the model.
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.Accurate dating of musical instruments is a very easy and useful skill to learn.Whether the instrument was found at a yard sale or a museum, there are several signs that can confirm the authenticity of an instrument. Most notably, production dates have been penciled or stamped on the butt end of the heel of the neck of most guitars and basses. instrument production history, production dates have been applied to various components.