Just what the British thought as well.
For as long as it suited their purposes and for as long as they could hold on to it. Are you claiming "might makes right"? because that is a POV that most Lost Causers view with disdain.
Your attempt to equate Ticonderoga with Sumter fails the sniff test. Sumters ownership was never in question right up until the rebels seized it. Although built within the boundary lines of the state of South Carolina it was ceded to the United States government in perpetuity. It was never legally the property of anyone except the USA.