Historical clue formulations

• Cusp — 2026-08-12
• Lip — 2025-09-06
• Verge — 2022-07-10
• Cliff's edge — 2019-11-19
• Threshold — 2019-01-09
• Lip — 2015-09-25
• Edge — 2012-01-23
• Threshold — 2011-04-28
• Verge — 2010-01-05
• Cliff's edge — 2006-03-26
• Critical point — 2000-10-01