The rules for Ryosei province were greatly amended before the Nara period and in the Meiji period, but they were not changed in the long term between Heian period and Edo period.
令制国は、奈良時代までと明治時代に大きな改廃がなされたが、その間の平安時代から江戸時代までの長期にわたって変更がなかった。