retcon

Etymology
A. The term retroactive continuity was popularized by comics writer, who was known for writing superhero comic books set decades in the past such as , and attributes it to an anonymous source.

Noun

 * 1) A situation, in a soap opera or other fiction, in which a new storyline explains or changes a previous event or attaches a new significance to it.

Verb

 * 1) To employ such a device.
 * 2) * 2006, Len Wein, ed., The Unauthorized X-Men: SF and Comic Writers on Mutants, Prejudice, and Adamantium 92:
 * Retroactive continuity (aka retconning), would reveal that Quicksilver and Scarlet Witch are also Magneto's children, showing that this was a guy who was really committed to his cause
 * 1) * 2006, Michael Eury, Daniel (CON) Best, Glen (CON) Cadigan, Mike (CON) Esposito, David (CON) Mandel, The Krypton Companion, p. 157:
 * Luthor appeared a handful of times, Gary "retconned" the Toyman and created Terra-Man, and Superman would get a worthy opponent whenever Len Wein did a fill-in.
 * 1) * 2006, Michael Eury, Daniel (CON) Best, Glen (CON) Cadigan, Mike (CON) Esposito, David (CON) Mandel, The Krypton Companion, p. 157:
 * Luthor appeared a handful of times, Gary "retconned" the Toyman and created Terra-Man, and Superman would get a worthy opponent whenever Len Wein did a fill-in.