Historical clue formulations

• Hush-hush — 2013-05-31
• Privately — 2012-03-27
• Covertly — 2005-04-30
• Without anyone knowing — 2004-05-14
• Secretly — 2003-12-27
• Not openly — 2003-04-06
• Secretly — 2000-08-25
• Secretly — 1997-07-05