Historical clue formulations

• Highly significant, as a stretch of time — 2024-05-25
• Momentous — 2021-08-21
• Of a historic period — 2019-12-24
• Era-defining — 2019-09-10
• Historically significant — 2018-01-30
• Momentous — 2017-06-10
• Extremely significant — 2004-12-05
• Momentous — 2001-01-21
• Extremely important — 1994-04-23