Flag Day

...However, since there were no rules at the time, there were various variations in the arrangement of the 13 stars. This June 14th is now a national holiday known as Flag Day. The stars and stripes were eventually changed to 15 stars and stripes when Vermont and Kentucky were admitted as states, but in 1818, five more states were added, so Congress decided to keep the 13 red and white stripes unchanged and to increase the number of stars as the new states were admitted, and set the date for adding new stars as Independence Day (July 4th) of the year following the new state's admission.

*Some of the terms mentioned in "Flag Day" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…ただし当時はなんの規則もなかったので，13星の配置にもいろいろの変形があった。この6月14日は現在〈旗の日Flag Day〉として祝日となっている。星条旗はやがて，バーモントとケンタッキーの州昇格によって，15星15条に変えられたが，1818年に至りさらに5州が増加したため，議会は，赤白13条を不変のものとし，星の数は州の増加に伴って増すことを定め，新たな星を加える期日は，新州が承認された次の年の独立記念日(7月4日)とした。…

※「Flag Day」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報