No, secession does not need to be valid for West Virginia to be entered as a valid state. When a state enters insurrection, the US does not lose the territory, rather, its state government institutions lose legitimacy, and its land area reverts to being a territory. As a territory, the Congress has the authority to set boundaries and to establish state governments, which the Congress did. Congress retains the right and duty to directly rule areas in insurrection, because of the constitutional guarantee that each state has a republican form of government.
Just as the boundaries of Ohio, Indiana, Michigan, and Illinois were set by the Congress, and state governments in those territories were established.
This is utterly incorrect, both in the theoretical and the factual. Virginia was one of the colonies which won independence from Britain and was indeed a State before the Congress ratified the Constitution, or even the Articles of Confederation. -- If it were to 'revert', then it must needs be revert to an independent State [read nation].
As a territory, the Congress has the authority to set boundaries and to establish state governments, which the Congress did. Congress retains the right and duty to directly rule areas in insurrection, because of the constitutional guarantee that each state has a republican form of government.
This also is incorrect.