Serial numbers for these guitars is not a perfect science, but in nearly all cases after Matsumoku's involvement they can be trusted to indicate what year the guitar was produced.
Shiro Arai Co.
Guitars produced by Matsumoku
Nearly all guitars produced by Matsumoku (beginning sometime late 1976 or early 1977) bore serial numbers indicating the year and possibly production sequence. A small number of guitars produced had serials preceeded by a letter, but as to what the letter inidicated is yet a mystery and one can only guess without concrete evidence. I have seen both 6 and 7 digit serial numbers (excluding the letter if it is present).This new serialization covered Aria, Aria Pro II, Vantage, Westbury, most Westones, Japanese Washburns, some Electras, and the Skylark as well as others.
The first digit (and upon rare occasion the first two) indicated the year. There is an inherent flaw with this single-digit method as the single digit year indicator will re-cycle after a decade! Attention must be paid to when the particular model was available and apply that to the first digit of the serial, excluding the letter if present. A bit of cross referencing is required. For example, my first Cardinal CS-350 has the serial 2010237 which indicates both by the first digit and the duration of the Cardinal CS-350 run it is a 1982 (and I know it is, I bought it then!). In rare instances the first two digits would indicate the year, in which case we can safely assume that my Cardinal is not a 1920! Had it been the two-digit version it would have begun with 82XXXXX rather than 20XXXXX, which would also indicate 1982.
Spotting and identifying early Korean models after production shifted to Korea...