Historical clue formulations

• Sounding good, as a musical instrument — 2026-04-27
• Best way to sing — 2025-05-21
• Not sharp, perhaps — 2021-09-26
• Not off key — 2021-01-27
• Connected (with) — 2016-02-27
• Pleasant way to play — 2010-01-02
• Perfectly pitched — 2006-08-08
• Not flat at all — 2003-07-24
• Jibing — 2002-12-07
• Properly pitched — 2001-07-02
• Pitched perfectly — 2001-02-24
• Without a sour note — 1999-02-10
• What musical instruments should be — 1998-06-01
• Like good pianos — 1996-05-10
• Pitched properly — 1995-12-09