Historical clue formulations

• Perry Como or Bing Crosby — 2025-12-20
• Bing Crosby or Nat King Cole — 2025-03-24
• Ol' Blue Eyes, e.g. — 2024-04-21
• Piano bar mainstay — 2022-11-26
• Robert Goulet, e.g. — 2014-12-12
• Bing Crosby, e.g. — 2010-09-14
• Dean Martin, for one — 2008-07-31
• Bing Crosby or Rudy Vallee, e.g. — 1997-04-21
• Balladeer — 1996-07-06