So, if you were born before the final change to the state’s Constitution and acceptance into the Union, are you a Natural Born Citizen of the US or not?
Yes. Barry Goldwater settled that question 50 years ago.
The Dakota Territory was an organized, incorporated territory. This means it was a fully integrated part of the national territory of the United States. All provisions of the Constitution fully applied there. Every person born there was a natural born citizen, except Indians.
Until the Constitutionally questionable Insular Cases, in the early 20th Century, there was never a question that the residents of all territories were fully defined as citizens just as were the citizens of each State.
The insular cases created the constitutionally questionable distinction between incorporated territory and unincorporated possessions.