Historical clue formulations

• Deepest, as feelings — 2019-07-18
• Like Mercury among all the planets — 2019-03-13
• Central — 2011-07-30
• Nearest the heart — 2008-08-17
• Closest to the center — 2008-07-18
• Hardest to get at — 2007-06-23
• Deepest — 1999-09-22
• Deeply personal — 1997-05-09