I also just think that the guy making the calenders was working on them, got to the date at the end, and then this happened:
Friend of calender maker guy: "Hey, Steve, how long have you been doing this?"
Steve/Calender maker guy: "Four years and ten months, why?"
Friend of calender maker guy: "Come on, get up, you've been working way to long. We're getting you a few beers, a hooker, and some of the finest River People nose candy feathers can buy."
Steve/Calender maker guy: "Okay, just let me finish up here..."
Cortez: "I am Cortez. I come from the mighty Spanish empire, surrender your gold, Godless heathens!"
Steve/Calender maker guy: "Okay, just let me *cough* get the *cough* Ho nos, I have Spanish flu I need *dies*"
Friend of calender maker guy: "No, now Steve can never finish the calender! Now future generations will think that the end of days is then, when really it's *get's shot by Cortez*"