Suppose that when humans begin to colonize other worlds the US is still alive in one form or another. Won't that mean that there will be many additional states being brought into the union, and thereby many additional stars to the US flag?
A solution may be to start counting plantets or star systesms with US territories for each star. This one proposes 27 systems with the star in the center representing Sol or Earth.
Plus it looks cool The Outer ColoniesThe Inner ColoniesColonial Mars