Historical clue formulations

• Rarely — 2015-02-15
• Not often — 2015-01-05
• Once in a blue moon — 2014-07-10
• Hardly ever — 2013-10-08
• Rarely — 2012-03-26
• Rarely — 2011-09-06
• Scarcely — 2010-08-19
• Only now and then — 2009-05-19
• Only now and then — 2004-02-01
• Rarely — 2003-01-16
• Infrequently — 1999-11-16
• Inhabitually — 1999-08-15
• Rare — 1999-05-15
• Only now and then — 1995-09-15
• Infrequently — 1995-03-30
• Infrequently — 1994-08-09