So you're writing a resume or a CV or a biographical sketch. What do you need to say to make you into a superhero with a fantastic back story that hints at your future greatness?
Retcon comes from "retroactive continuity", a plot device first used in comic books. See Urban Dictionary for a fun definition.
I have a sneaking suspicion that once I go back far enough and create some retroactive continuity that I'll be able to describe my life as a set of 30-year projects, many of which are already in progress and that run in parallel and not just one after the other. Some short-term jobs can be reconned into parts of a longer narrative arc if you tell you stories right; that makes the resume shorter.
Goodness knows my work history is complex enough that some new hire HR operative is unlikely to make sense of it. Better to do the comic book treatment of it and cast myself in the best possible light for the circumstances.