Historical clue formulations

• "Parsifal" composer — 2020-04-23
• German composer of "Tristan und Isolde" — 2015-02-09
• Composer of the 17-Across — 2010-09-23
• Liszt's son-in-law — 2002-03-16
• Ring cycle composer — 2001-02-19
• 1950's-60's Big Apple mayor — 2000-04-23
• Much sought-after baseball card — 1994-09-23