In ANH Han Solo tells Luke and Ben that the Millennium Falcon can make the Kessel Run in less than 12 parsecs. Infamously a parsec is a unit of measurement and not a unit of time as Han appears to use it when referencing the speed of his ship.
The earliest retcon I'm aware of regarding this discrepancy is Lucas stating that Han was a bullshit artist and knew Ben and Luke wouldn't know the difference between the two but it sounded impressive. The later EU approach is that Han used the speed of the Falcon combined with his piloting skills to map a new route that cut down the normally 20 parsec run to just 12 parsecs.
Which retcon do you prefer? Which seems more in line with Han's character, a cocky bullshit artist or a talented smuggler sure of his abilities?