Over the years Fender used modular production techniques that may have resulted in a guitar that has parts from one year to another.
Clearly Fender wasn’t afraid to use incorrect parts when they were in a bind. The 5G12 Concert is the earliest version from very late 1959 and early 1960 so the existence of a tweed example, while extremely rare, is certainly plausible since Fender was making lots of tweed amps during the same time period.
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.
While this neck dating is useful in roughly determining the age of a guitar, it is certainly not definitive.
Dating a Fender Guitar by it’s Serial Number can be a little tricky.
In most cases you can only get a ball park range for your production date.