Historical clue formulations

• Four: Prefix — 2012-12-04
• Half of oct- — 2010-10-15
• Numerical prefix with oxide — 2009-08-12
• Four: Prefix — 2009-08-10
• Four: Prefix — 2008-06-29
• Having four parts: Prefix — 2004-10-31
• Four: Prefix — 2002-12-26
• Fourfront? — 1997-05-25
• Four: Prefix — 1994-06-19