What do Japanese emperors have to do with the date codes of guitars? More than you think.
Many Yamaha guitars without valid serial numbers have ink stamped date codes on the inside. Japanese dates are based on eras of the reigning emperors (Meiji, Taisho, Showa, Heisei). The first 2 digits of the code are the year based on the SHOWA period, the reign of Emperor Hirohito 1926 - 1989. Year 1 is 1926, therefore the 45th year of his reign is 1970. Then the 2 digit Month. Then the 2 digit Day. Year.Month.Day 45.12.28 equals December 28th, 1970.