"When new states were admitted, it became evident, that the flag would become burdened with stripes. Congress thereupon ordered that after July 4, 1818, the flag should have 13 stripes, symbolizing the 13 original states; that the union have 20 stars, and that whenever a new state was admitted a new star should be added on the July 4 following admission. No law designates the permanent arrangement of the stars. However, since 1912, when a new state has been admitted, the new design has been announced by executive order. No star is specifically identified with any state."
THE WORLD ALMANAC and BOOK OF FACTS 1998
S. 526
Einen neueren Almanac habe ich leider zur Zeit nicht, aber das wird auch nichts Genaueres beschrieben sein.
Der Almanac, wie auch der der NY Times, ist im übrigen sehr zu empfehlen.