Well, Hernan P.Burgos above said, "At this time Miyata used to have the date on the serial number R 937(year), now the first letter is the year."

"93" can't be a year so it'd be a strong guess that "9" is the month. Then we have "37" for the year: You just have to find out if Miyata was using the evil western calendar in 1937, an era of very strong Japanese nationalism and imperialism, or if they were using the Japanese calendar (in which case "37" means Showa 37 which was 1962).