You need to read the Constitution a little more carefully.
They specifically exempted themselves as they were Citizens at the time the Constitution was signed.
They exempted THEMSELVES as “citizens at the time of the adoption of the Constitution” - what about those born between when the Constitution was adopted and when England no longer considered all Americans as English (after the war of 1812)?
Was anyone born between those times, even if born of two American parents on American soil - not an NBC because England considered them English?