I visited Dachau in 1969 and saw this:
http://www.scrapbookpages.com/DachauScrapbook/MemorialSite/index.html
I'm not sure but I think Elie Wiesel made the famous speech in 1999.
I'm also not sure when "NEVER AGAIN" was cast in stone but I think it was sometime between 1956 and 1965.