Such a change could be seen as early as the end of the Heian period and the Muromachi period but was not common yet, and gradually became generalized through the Muromachi and Edo periods.
平安末期や鎌倉時代には既に例が見られるが、まだ一般的ではなく、室町時代、江戸時代を経てゆっくりと一般化していった。