Historical clue formulations

• Key of Bach's "The Art of Fugue" — 2021-08-03
• Key of Beethoven's Ninth — 2021-03-31
• Key of Mozart's "Requiem" — 2019-08-09
• Key of Dvorák's Symphony No. 7 — 2018-01-04
• The saddest key, supposedly — 2010-02-14
• Key of Beethoven's Ninth — 2008-07-14
• Key of Mozart's "Requiem" — 2003-06-08