The Constitution was written in 1787. The first translation of Vattel to use NBC was in 1797. And it was a poor translation of the word “indigene” - which happens to be an English word, as well as French.
That NBC is the equivalent of natural born subject is shown by the Massachusetts legislature:
“In February, 1785, the Massachusetts legislature passed “AN ACT FOR NATURALIZING NICHOLAS ROUSSELET AND GEORGE SMITH.” in which it was declared that Nicholas Rousselet and George Smith “shall be deemed, adjudged, and taken to be citizens of this Commonwealth, and entitled to all the liberties, rights and privileges of natural born citizens.”
In July, 1785, the Massachusetts legislature passed “AN ACT FOR NATURALIZING MICHAEL WALSH.” in which it was declared that Michael Walsh “shall be deemed, adjudged, and taken to be a citizen of this Commonwealth, and entitled to all the liberties, rights and privileges of a natural born citizen.”
In July, 1786, the Massachusetts legislature passed “AN ACT FOR NATURALIZING JONATHAN CURSON AND WILLIAM OLIVER” in which it was declared that Jonathan Curson and William Oliver “shall be deemed adjudged and taken to be free Citizens of this Commonwealth, and entitled to all the liberties, privileges and immunities of natural born citizens.”
In March, 1787, the Massachusetts legislature passed “AN ACT FOR NATURALIZING WILLIAM MARTIN AND OTHERS.” in which it was declared that William Martin and Others,”shall be deemed, adjudged and taken to be free Citizens of this Commonwealth, and entitled to all the liberties, privileges and immunities of natural born subjects.”
In March, 1787, the Massachusetts legislature passed “AN ACT FOR NATURALIZING EDWARD WYER AND OTHERS THEREIN NAMED.” in which it was declared that William Martin and Others,”shall be deemed, adjudged and taken, to be free Citizens of this Commonwealth, and entitled to all the liberties, privileges and immunities of natural born subjects.”
In October, 1787, the Massachusetts legislature passed “AN ACT FOR NATURALIZING BARTHOLOMY DE GREGOIRE, AND MARIA THERESA, HIS WIFE, AND THEIR CHILDREN.” in which it was declared that Bartholomy de Gregoire, and Maria Theresa, his wife, their children,”shall be deemed, adjudged and taken to be free Citizens of this Commonwealth, and entitled to all the liberties, rights and privileges of natural born citizens.”
In November, 1787, the Massachusetts legislature passed “AN ACT FOR NATURALIZING ALEXANDER MOORE, AND OTHERS, HEREIN NAMED.” in which it was declared that Alexander Moore and others,”shall be deemed, adjudged and taken to be free citizens of this Commonwealth, & entitled to all the privileges, liberties, and immunities of natural born subjects.”
In June, 1788, the Massachusetts legislature passed, “AN ACT FOR NATURALIZING WILLIAM MENZIES, AND OTHERS, THEREIN NAMED.” in which it was declared that William Menzies and others “shall be deemed, adjudged and taken to be free citizens of this Commonwealth, and intitled to all the liberties, privileges & immunities of natural born subjects.”
In November, 1788, the Massachusetts legislature passed, “AN ACT FOR NATURALIZING ELISHA BOURN, AND OTHERS, THEREIN NAMED.” in which it was declared that Elisha Bourn and others “shall be deemed, adjudged and taken to be free Citizens of this Commonwealth, & entitled to all the liberties, privileges & immunities of natural born Citizens.”
In February, 1789, the Massachusetts legislature passed, “AN ACT FOR NATURALIZING JAMES HUYMAN, AND OTHERS, THEREIN NAMED.” in which it was declared that James Huyman and others “shall be deemed, adjudged and taken to be free Citizens of this Commonwealth, and entitled to all the Liberties, Privileges and Immunities of natural born subjects.”
In June, 1789, the Massachusetts legislature passed, “AN ACT FOR NATURALIZING NATHANIEL SKINNER, AND OTHERS, THEREIN NAMED.” in which it was declared that Nathaniel Skinner and others “shall be deemed, adjudged and taken to be free citizens of this Commonwealth, and entitled to all the liberties, privileges and immunities of natural born subjects.”
In March, 1790, the Massachusetts legislature passed “AN ACT FOR NATURALIZING JOHN JARVIS, AND OTHERS, THEREIN NAMED” in which it was declared that John Jarvis and others, “shall be deemed adjudged and taken to be free citizens of this Commonwealth, and entitled to all the liberties, privileges and immunities of natural born subjects.”
Also in March, 1791, the Massachusetts legislature passed“AN ACT FOR NATURALIZING JOHN WHITE & OTHERS” in which it was declared that John White and others, “shall be deemed adjudged and taken, to be free citizens of this Commonwealth, and intitled to all the liberties, privileges, and immunities of natural born subjects.”
Notice one of the ratifying legislatures used NBS & NBC interchangeably. That doesn’t eave much doubt about how the ratifiers of the Constitution understood the term, does it?
And Ratified in 1789.
Look at your time-line. Almost everything prior to 1789 says 'subject' and everything after says citizen.
Until the Constitutional ratification process was complete, they were 'subjects'.
The States were accepting petitions from the people to be recognized as citizens so they could be in accordance with Article II Section I, clause 5
No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution
Of course you can give the appearance that they're 'interchangeable'. Particularly since they aren't in chronological order.