It's been my observation in American history, that generally, after the 40th anniversary of something, it goes downhill, mostly because many of those who were around at the time of an event, have died off.
The big remembrance seems to occur earlier, on the 20th or 25th anniversary, and then it declines after that, although it's still big up until and including the 40th.
Pearl Harbor and D-Day are good examplles.
I also give you the Kennedy assassination of 1963; does anyone recall seeing it marked last November 22? Even on Skins's island there was only one campfire about it, as compared with many about the 40th anniversary of the Kennedy assassination of 1968.
Tempus sure does fugit; sic transit gloria.