What Month Is Missing From The Calendar. With the upgrade to windows 11, we lost the calendar that displayed when we click on the date located in the lower right corner. Yes, there have been historical calendars and timekeeping systems that included 13 months in a year.

Despite what some people say, there was little backlash from the public. Here’s a brief explanation of how the calendar has evolved and why people in the past have actually “slept through” 10.