With four founding members, why are there three stars on the Federation flag?
The flag was designed long before the founding members were suddenly (see parent post) a settled fact:
> According to the Star Trek Sticker Book (Pg. 9), by Michael Okuda, "At one time, it was thought that the three bright stars in the starfield might represent Earth, Vulcan, and the Klingon Homeworld, since during early episodes of Star Trek: The Next Generation it was thought that the Klingons might have actually joined the Federation. When later episodes made it clear they had not, the three bright stars were left undefined."