Historical clue formulations

• Least polluted — 2020-04-16
• Most unspoiled — 2019-07-15
• Most unsullied — 2015-11-16
• Least tainted — 1998-08-31
• Least affected — 1998-05-23
• Least tainted — 1997-12-26
• Most perfect — 1995-10-15