From Gibson: From 1970-1975 the method of serializing instruments at Gibson became even more random. All numbers were impressed into the wood and a six digit number assigned, though no particular order was given and some instruments had a letter prefix. The orange labels inside hollow bodied instruments was discontinued in 1970 and were replaced by white and orange rectangle labels on the acoustics, and small black, purple and white rectangle labels were placed on electric models. In 1970, the words "MADE IN USA" was impressed into the back of instrument headstocks (though a few instruments from the 1950s also had MADE IN USA impressed into their headstocks as well). 1970, 1971, and 1972 100000s, 600000s, 700000s, 900000s 1973 ...........................000001s, 100000s, 200000s, 800000s and a few “A” + 6 digit numbers 1974 and 1975 ...........100000s, 200000s, 300000s, 400000s,500000s, 600000s, 800000s and a few A-B-C-D-E-F + 6 digit numbers During the period from 1975-1977 Gibson used a transfer that had eight digit numbers, the first two indicate the year, 99=1975, 00=1976 and 06=1977, the following six digits are in the 100000 to 200000 range. MADE IN USA were also included on the transfer and some models had LIMITED EDITION also applied. A few bolt on neck instruments had a date ink stamped on the heel area. In 1977, Gibson first introduced the serialization method that is in practice today. This updated system utilizes an impressed eight digit numbering scheme that covers both serializing and dating functions. As you can see, the serial number series repeats in some years. Pot codes are the best - look for 137yyww where yy=Year and ww=Week, eg 1377415 is the 15th week of 1974. Other things to note: - through 1974 necks were mahogany, in 1975 they changed to maple. Check under your truss rod cover. - through 1974 they used a trans tenon (see the FAQ tenon thread), in 1975 the short tenon started. BUT, some '75s and even '76s were made with a trans tenon. Pull the neck pickup, you can see the tenon if it's a trans, you cannot see a tenon if it's short.