Historical clue formulations

• Vietnamese currency — 2025-06-21
• Bell sound — 2015-01-20
• Vietnamese currency — 2014-03-13
• Doorbell sound — 2011-04-13
• ... a doorbell — 2008-12-02
• Steeple sound — 2004-06-12
• Tintinnabulation — 2001-07-06
• Vietnamese currency — 2001-03-11
• Bell sound — 2000-07-21
• Doorbell sound — 1999-10-11