Historical clue formulations

• So-so — 2020-05-25
• The "A" of D.J.I.A. — 2019-11-25
• C-worthy — 2019-10-14
• Mean — 2017-10-01
• About 25 years, for N.F.L. players — 2016-10-13
• C-worthy — 2015-09-04
• Just O.K. — 2012-01-31
• C-rated — 2011-11-15
• C — 2011-09-11
• Mean — 2010-12-02
• So-so — 2010-07-11
• C, say — 2010-02-10
• C — 2009-12-27
• Ho-hum — 2006-03-10
• Less than outstanding — 2005-05-29
• Less than stellar — 2004-06-18
• Unremarkable either way — 1999-02-07
• B+ or C-, e.g. — 1998-12-05
• Garden-variety — 1998-05-10
• Fair — 1997-05-11
• See 55-Across — 1997-05-04
• Middling — 1995-02-08
• Garden-variety — 1994-06-12
• Nothing special — 1994-04-18