There was indeed a calendar change just 4 years after the 1748 almanac you were reading. In 1752 the American colonies switched from the Julian to the Gregorian

There was indeed a calendar change just 4 years after the 1748 almanac you were reading. In 1752 the American colonies switched from the Julian to the Gregorian calendar. That leaped 11 days ahead. https://en.wikipedia.org/wiki/Adoption_of_the_Gregorian_calendar https://en.wikipedia.org/wiki/Adoption_of_the_Gregorian_cale...