September 24th, 2014.
To know the date of publication of a given xkcd comic, go to https://xkcd.com/archive/, search for the title you're after, then the date of publication is displayed in the mouse-over text.
To know the date of publication of a given xkcd comic, go to https://xkcd.com/archive/, search for the title you're after, then the date of publication is displayed in the mouse-over text.