United States (1795-1818)
Before 1818, there was no established procedure for updating the American flag. Congress passed a law in 1795 adding two more stripes and stars (representing Vermont and Kentucky) to the original flag, but didn’t bother to update it again when Tennessee became a state the following year. The “Star-Spangled Banner" seen by Francis Scott Key during the War of 1812 was a 15 star flag, even though the country had 18 states by that point.
By 1818, the United States had 20 states and non-standard flags proliferated. Congress finally settled on the one star per state formula but went back to 13 stripes to represent the original Thirteen Colonies.