Around the middle of 1964 major changes occurred. The info below is very useful for dating a Gibson guitar in cases where serial numbers were repeated or unclear.
1. Neck width at the Nut was reduced from 1 11/16 inches to 1 9/16 inches (you will see cases of 1 10/16 inches during this transition year.
2. Most Hardware moved from Nickel plated to Chrome, this included bridges, tuners and tailpieces.
3. Most serial numbers moved from 5 digits to 6 digits.
4. Kluson Tuners were stamped with 2 lines down the back instead of one line down the center of the back with the words Kluson Deluxe.
5. By 1965 the Stud Tailpiece on the Gibson Es-335, Es-345 and ES-355 were removed and replaced with a Trapeze tailpiece.
There is more information here on the our Guitar identification Page.
Gibson used Factory Order Numbers (FON) on some of their guitars from about 1908 to 1961. Many times you will see both a factory order number and serial number. The FON was stamped for each batch in production and each instrument in the batch during the early stages of the build.
The FON can be very helpful dating the instrument as that might be the only marking. They can also be used together with the serial number to more precisely date the instrument.
Gibson used four different patterns of FON’s through out the years.
The first FON’s are usually ink-stamped on the neck block inside the body and have of a three to five digit number with no suffix
Alphabetical FON: 1935-1942
A for 1935
B for 1936, and so on
This method stopped around 1942 .
FON after WW II: 1949-1952
After WW II FON’s were hit or miss and not very good for dating or not present on the guitar. When present they were rubber stamped on neck block or on back of the headstock with numbers from 100 to 9999.
Alpha FON: 1952-1961
Around 1952 Gibson went back to the a first letter pattern
The first letter used in
1952 was Z
Y in 1953, etc.
Then lastly Q in 1961 which is very rare to see.
1968 -69 were dark years for Gibson and the Norlin Corporation buy out began. Gibson needed revenue and to use up old parts. Less than perfect tops used to make the J-45 and B-25 were sprayed a solid color of red or black and a few brown . A white screwed down pickguard was used. Many of the instruments were 4 piece tops and marked seconds. Late in 1968 the bridge was reversed with the belly facing down , and the Gibson logo on the pickguard was removed. There is more Gibson Acoustic Flattop Model Information here.