Factory Order Numbers (FON) with a letter from 1935 to 1941.FON consists a batch number of usually four digits, followed by a one letter (sometimes prefixed by a space) followed by one or two digits (ranking).Gibson has used various methods of numbering from 1900, so it is not simply based on the serial number to identify the year of manufacture..From 1902 to 1976, Gibson instruments have a serial number or a FON (Factory Order Number) or both.1935-1937: Letter between the batch number and the order number. 0123 A5 1938-1941: Two or three letters before batch number. If there is a second character follows it is the code for the type of the instrument.(G = Gibson, K = Kalamazoo, W = Recording King (Montgomery Wards).
It's best when trying to evalute a collectible to contact Gibson for further information that is not as easily available.
in 1947 Gibson changed the serial number pattern and in 1954 went from white labels to orange labels.
Since all the instruments using this serial number pattern were acoustic or semi-hollow the labels were located inside the instrument body.
A new system was put in place in 1961 which was set up to include all the Gibson instrument lines.
Serial numbers show approximate date of manufacture.