The Okinawa study had even bigger issues, most notably age misrepresentation linked to the loss of koseki registers during WW2, which were unreliable to begin w

The Okinawa study had even bigger issues, most notably age misrepresentation linked to the loss of koseki registers during WW2, which were unreliable to begin with and were reconstructed from family testimony after the war. I remember reading that on the top of all the rest, elderly people there tended to make mistakes of a full 12 years when giving their age because they would base themselves on their year sign, which they were more familiar with than the new Western calendar.