Historical clue formulations

• The highest form of flattery? — 2021-11-20
• Level off at a higher point — 2021-05-24
• Reach a point of diminishing returns — 2019-10-25
• Neither improve nor decline — 2015-12-31
• Stop getting any higher — 2014-11-11
• High level — 2014-08-09
• Level off — 2014-02-06
• Stop getting better — 2013-09-08
• Flat part of a chart line — 2002-12-23
• Tableland — 2002-06-04
• Level off — 2001-07-13
• Steady high — 1996-04-21