I am not sure about this one in particular, but yes, bonus event that got added later got their own episode number.
In season 1 the christmas event was numbered episode 33, I think.
If you finished the story and have something white and shiny in MCs living room now, all there is left to do is to find the rest of the hidden events.
Mind you, that Halloween and Christmas require you to set the date on your PC in order to unlock them (once unlocked, they can be played anytime through the replay menu).
The commercial distributions of the games (GOG, Steam) don't need any unlock codes.