The Queen of England gets two birthdays, so why shouldn't old George W.? :^)
From the royal web site -
The Queen celebrates two birthdays each year: her actual birthday on 21 April and her official birthday on a Saturday in June.
Official celebrations to mark Sovereigns’ birthday have often been held on a day other than the actual birthday, particularly when the actual birthday has not been in the summer. King Edward VII, for example, was born on 9 November, but his official birthday was marked throughout his reign in May or June when there was a greater likelihood of good weather for the Birthday Parade, also known as Trooping the Colour.
It can be a real mess when trying to figure out ages and birthdates for 18th c ancestors, or 17th c for that matter, and depending on where from, 19th and 20th c. The calendar adjustment is so far out of living memory, and probably never mentioned in American history classes (which concentrate on Black History Month, Herstory, and how all Republican Presidents were evil, except for Lincoln who was really a Democrat; wedged between self-esteem class and self-criticism class), that it's nearly as confusing and upsetting to some folks as when they learn about the history of US currency. :')