Historical clue formulations

• Border (on) — 2025-09-26
• Borderline — 2025-05-18
• Cusp — 2023-10-21
• Threshold — 2022-02-20
• Brink — 2018-01-23
• Threshold — 2015-12-14
• Brink — 2015-06-07
• Brink — 2014-04-29
• Brink — 2013-08-18
• Border — 2012-11-10
• Brink — 2009-03-30
• Threshold — 2008-12-14
• Border — 2006-11-18
• Margin — 2006-04-08
• Threshold — 2005-05-17
• Brink — 1999-12-09
• Brink — 1998-01-21
• Threshold — 1996-01-28
• Periphery — 1995-09-17