The birth announcement was posted 10 days after the birth occurred.
It will probably be known eventually that his mother filed for a birth certificate to get him registered as a US citizen as soon as she and baby got off the plane.
Why is it that all the other birth announcements were showing the same range of birth dates? Did all those mothers have to fly in their babies from foreign shores and register them, thus explaining the same time gap for Obama as all the other babies born from Aug 2 to Aug 7 published that day?