The former were supposedly works of the early period of Emperor Toba Insei period and the early 12th century, and latter during the Insei period of Emperor Goshirakawa of the late twelfth century.
前者は12世紀前半の鳥羽天皇院政前期、後者は12世紀後半の後白河天皇院政の頃の作品とも言われる。