Historical clue formulations

• Set of notes in a seventh chord — 2026-04-17
• Four of a kind, say — 2020-12-05
• Covalent bonds of a carbon atom, e.g. — 2017-10-08
• Group of four — 2017-03-08
• Foursome — 2013-01-27
• Four-note chord — 2009-11-07
• Foursome — 2009-09-02
• The classical elements, e.g. — 2008-05-30
• Monopoly's railroads, e.g. — 2006-12-02
• Cat's paws, e.g. — 2005-04-22
• The women in "Little Women," e.g. — 2002-07-27
• Foursome — 2000-02-03
• Four of a kind — 2000-01-13
• Foursome — 1999-05-03
• Foursome — 1998-11-29