Historical clue formulations

• Wavelength symbol — 2026-09-24
• Kappa follower — 2024-08-11
• Letter resembling an inverted "V" — 2010-11-10
• Sorority letter — 2008-11-16
• Leader of Lesbos? — 2008-07-20
• Upside-down V — 2004-11-26
• Sorority letter — 2003-09-07
• Kappa follower — 2000-07-25
• Kind of particle — 1997-02-02