Historical clue formulations

• In all honesty — 2025-06-15
• "Honest to goodness!" — 2025-03-18
• Without a doubt — 2024-06-09
• In fact — 2021-01-22
• In all honesty — 2020-07-23
• "I'm serious" — 2020-04-28
• "Cross my heart" — 2019-12-08
• "I kid you not!" — 2019-05-19
• In all honesty — 2019-04-16
• Yours ___ (letter sign-off) — 2017-12-11
• Without a doubt — 2015-04-03
• In fact — 2006-11-01
• Word immediately preceding some signatures — 2006-02-17
• "No kidding" — 2005-12-02
• "Yours _____" (letter closing) — 1995-04-24