[Lurking Libertarian]

The NBC clause was introduced before Naturalised Citizens existed in the US.

Nonsense. The states were naturalizing citizens under the Articles of Confederation, which is why the Constitution gave Congress the power to establish a "uniform Rule of Naturalization" (Art. I, sec. 8, cl. 4).

[plenipotentiary]

If the Constitution meant Naturalised Citizens couldn’t be President, why did they invent the term “Natural Born Citizen”?