Historical clue formulations

• Zero, zip, nada — 2020-01-14
• Zero — 2019-02-21
• Zip — 2015-09-25
• Zero — 2015-08-06
• Zip — 2006-08-27
• Zero — 2005-03-05
• Less than any — 2003-07-05
• Zip — 2002-11-22
• Zip — 2002-11-01
• Opposite of all — 1995-12-17