Here is a summary of ownership of Fort Sumter.

http://www.civilwarhome.com/sumterownership.htm

Seems like a good bit of digging would have to be done to get to the whole truth, or we can just accept what we read and believe it. We could accept the authors summary "The War Department became concerned in the 1890s that they might not have clear title to all of their various installations, so they ----"

To my way of thinking this treaty was good as long as South Carolina was part of the Union.

GP