A guitar neck could have been produced in 1956, then slapped onto a body in 1957 and if late enough in the year pickups may have been put in early 1958.The best option for getting a close production date is to remove the neck from the body.
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.
These serial numbers did not identify the country of origin in the body of the number.
Instead, the instrument’s country of origin appears on the decal on the back of the headstock, near the serial number.
The neck date simply refers to the date that the individual component was produced.
Given the modular nature of Fender's production techniques, an individual neck may have been produced in a given year, placed in the manufacturing warehouse and remained in stock for a period of time, and then subsequently paired with a body to create a complete guitar in the following year.