You introduce an interesting nuance of the definition of NBC. The citizenship of the initial several presidents, of course, is not relevant - they became citizens the minute the gavel finally dropped in the 1787 Constitutional Convention. On the other hand, what is relevant is the citizenship of their parents
Arguably the initial presidents could have been NBC's had they been born to parents who were citizens of the ratifying states prior to 1787 - but clearly the founders did not agree with that view and thought they had to provide two separate options with the latter applicable to only those candidates alive at the adoption. If a candidate was not alive on the first day of the nation, the NBC requirement applied.
I think the arguments based on this article have diverged from the real point.
The question, to me, is who became a natural born citizen via the ratification of the Constitution and who was already a natural born citizen via the Declaration of Independence? Who were the "gap" citizens?
The first seven Presidents were citizens of their respective states on the day the nation was born, making them automatically natural-born when the nation was naturally born. At the founding of the nation, the citizenship of their parents was irrelevant -- all original citizens were, by definition, natural born.
Where I believe your statement that I cited at the top is misguided (and your whole post, frankly) is the notion that "they became citizens" via this clause in the Constitution. They did not. This was an eligibility clause for the presidency, not a grant of citizenship to people in the United States at the time of ratification. All it did was grant people who became citizens in their states between July 5, 1776 and June 21, 1788 an exception to the "natural born citizen" requirement to become President.
Think of it this way: the Constitution has a ban on "ex post facto" laws, meaning that no law can be passed that retroactively puts someone in conflict with it. The "natural born citizen" requirement to become President can be seen as an ex post facto law to anyone who was a first-generation child of immigrants to the United States after July 4, 1776. Therefore, this exception to the "natural born citizen" requirement was necessary to keep it from becoming an ex post facto punishment to recent citizens who were governed under the Articles of Confederation and the constitutions of the several states.
The "natural born citizen" requirement to become President would only be fully operative to people born in the United States after June 21, 1788.
-PJ
July 4, 1776. The courts have consistently held that American citizenship began the day Congress officially declared Independence from England.
One such court case is Inglis v. Trustees of Sailor's Snug Harbor, 28 U.S. 99 (1830).