Historical clue formulations

• Prefix with -gram — 2018-04-13
• 18-Across plus one — 2015-09-19
• Numerical prefix — 2012-06-13
• Prefix with 6-Down — 2008-02-01
• Tetra- plus one — 2006-09-12
• Prefix with -gon — 2006-07-17
• Prefix with -gon — 2004-08-03
• Numerical prefix — 2003-09-05
• Five in front — 2003-03-01
• Five: Prefix — 2002-12-16
• Five: Prefix — 2002-04-15
• Prefix with -hedron — 2001-10-14
• Prefix with -gon — 2001-09-25
• Prefix with meter — 2001-04-29
• Tetra- plus one — 2000-03-22
• Prefix with dactyl — 1997-05-25
• Prefix with -gon — 1996-05-29