Historical clue formulations

• Musical note that's a step and a half below A — 2021-07-19
• Key for Debussy's "La fille aux cheveux de lin" — 2021-02-22
• Black piano key — 2018-01-06
• Black piano key — 2006-09-24
• Key of Chopin's "Butterfly" Étude — 2005-04-07
• A black key — 2004-08-01
• Chopin's fifth étude is in it — 2004-03-27
• Chopin's Polonaise No. 16 in ___ — 2001-01-22