Yes, old notes remain as legal tender in Japan. For example, one yen note which was issued in 1885 still remains legal tender as far as the Japanese government is concerned. As far as the Japanese government is concerned, the 1885 one yen note is still valued as one yen. However, among collectors, the 1885 one yen notes are valued at 35000 yen for an average condition and 120000 yen for a pristine condition.

Talk about old notes no longer vaild... Earlier this year I had a transit at LHR, transit was about four hours. I had British Pond notes left over from my travel to the U.K. back in 2016. I was thinking I can buy shortbread, tea, etc. at LHR Terminal 5 during my transit using the British Pond I had. Well..., during the transit I found out that I can no longer use the British Pond notes I had. Currency exchange at the terminal said they do not exchange old British Pond notes.