Board Thread:Questions and Answers/@comment-3074300-20170126190128/@comment-27441457-20170126190511

Shadis' tone suggests that he's uncertain of his own claim that it happened twenty years ago. Because of the 13-year curse, Grisha couldn't have been within the Walls for longer than that. Since he went with his choice to attack the royal family in the year 845, assuming he'd reached his final year, this means he would have arrived in the Walls in 832. 18 years is pretty close to 20, so Keith was just uncertain of the timespan. It could be that he hadn't seen Grisha for several years after finding him, which would've thrown off his memory of how long he'd known him.