Historical clue formulations

• Result of not following through (of which there are four examples in this puzzle's grid) — 2013-02-06
• Moral lapse that is reflected literally by the answers at 17-, 24-, 46- and 54-Across — 2012-03-08
• ... in 12-/35-Down — 2011-07-31
• Description of 25- and 26-Across — 2003-07-13