Letters in the serial numbers often represent specific numbers that in turn stand for the month and year of manufacture.
For example L=5 which may mean the year of manufacture in this case 1985 or the 5th month of the year, May.
The first letter indicates the last digit of the year of production. Tenryu/Wada Factory, Made in Japan, 1985-1986: ######.
Example: hm02316 = the 316th unit made on June 2 of 1961, 1971, 1981, 1991, or 2001. If you still can’t figure it out, please see Yamaha contact info at the bottom of this page. Tenryu/Wada Factory, Made in Japan, 1969-1984: ######.
Custom Shop, Made in Japan, 1966-1985: 001-1042 in sequence Custom Shop, Made in Japan, 1986-1990: Letter-####, like so: J7012.
Another mystery surrounds SG200's and SG300's made in Japan.
These guitars have serial numbers that don't match any of Yamaha's record.
Simply find the range of serial numbers that includes yours, and match it with the corresponding year.