FONs are often not sequential and Gibson also apparently re-used some of them.
The age of a Gibson guitar, along with the physical condition and relative rarity, are the major factors in determining its value.
While physical condition can be assessed with a careful inspection, rarity and date of manufacture are not always easy to determine.
So far all the inked numbers seem to begin 01, 10, or 11, ie the very years for which the confusion exists (see table & comments above).
Until recently it was thought these inked numbers were all from guitars made in the late 1990's or 2000's, and possibly made outside the main Tokai factory (maybe in Korea).
Inked numbers are discussed separately below the main list.