The numbers and decals are produced far in advance, and apparently, some N9 decals, (which were supposed to be used in 1999), were affixed to some instruments in 1990.As a result, you will see some 1990 guitars bearing N9 serial numbers.So, obviously a neck date, while being helpful in providing a date range of production, it cannot be a definitive reference.
With 1990 came the introduction of the "N" prefix serial numbers, which stood for the 1990s.
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.
This chart contains If you are unable to place the approximate year of manufacture of your instrument using the above charts, there are a few great books available, which have invaluable information on the history of Fender instruments.
If you have serious interest in learning about the history of Fender instruments, or if you just want to try to establish the year of production of your own axe, we would highly recommend that you pick up one or more of the following books.