Short answers, pulled from the story.
The Confederate government of Missouri began operations in 1861 after pro-Confederate legislators gathered in Neosho during the autumn. The legal status of this ordinance remained unaccepted by Missouri's Union supporters from that day forward.
The exiled administration established operations in Marshall, Texas instead of remaining in St. Louis. Their jurisdiction extended only as far as Confederate military strength could reach.
Governor Claiborne Jackson and other secessionists met in Neosho later that fall to act as the Missouri General Assembly despite Union opposition. They enacted an ordinance of secession on the 28th of October 1861.
The Confederate government of Missouri ceased to exist following the surrender of all Confederate troops west of the Mississippi River at New Orleans on the 26th of May 1865. No further operations occurred after the surrender date ended organized resistance.
This admission made Missouri the purported 12th state of the southern alliance when supporters received it on the 28th of November 1861. The state was represented by the twelfth star on the Confederate flag.