The eleven star flag became official on July 2, 1861 following admission of Tennessee to the Confederacy.

Missouri was admitted on November 28, 1861. Upon admission of Kentucky on December 13, the thirteen-star flag became official. [The Flags of the Confederacy by the late Devereaux D. Cannon, Jr.]

Later, a fifteen star flag appeared which I believe represented the states of California and New Mexico, though not official, nor in the Confederacy.

A good read on the Maryland situation is that of a fairly new book, "Allegiance, Fort Sumter, Charleston and the Beginning of the Civil War," David Detzer.

George Martin