If you are going to ask what NBC means, you also need to ask what does the enumerated power of Congress “to establish an uniform Rule of Naturalization” mean.
No law written by Congress changes the Constitution.
Natural born citizen means born here of citizen parents, same as when it was written into the Constitution.
One is NATURALLY a US citizen ONLY when one CANNOT be anything else.
No foreign birth
No foreign parent(s)
No foreign citizenship(s)