of Missouri was illegitimate, but the Union convention was?
The Union response in Missouri was to organize a state convention, which declared the state government to be deposed, and organized a provisional state government. As a result, Missouri had two state governments: the elected government which seceded and joined the Confederate States, and the provisional government created by Unionists to remain with the United States.
I'll add quote from Wikipedia:
https://en.wikipedia.org/wiki/Confederate_States_of_America
The government of the United States (the Union) rejected the claims of secession and considered the Confederacy illegitimate.
So no state actually seceded because it wasn't recognized by the Union or in the case of Missouri - a Union convention?????????