http://www.thewrap.com/mike-molly-last-minute-holiday-episode-is-a-christmas-miracle-exclusive-video/

A holiday episode wasn’t originally planned until CBS released the air dates, and the cast and crew realized there was an episode airing a few days before Christmas.
Read more at http://www.hitfix.com/tv-tattle#TC8lx1DExwf5kkya.99