In a translaltion about the Roman Republic. You have just highlighted why the term was not used in legal discussion and why it was used by Vattel and others who were read by the founders in relation to republics. The word uused in law cases and treatises was “subject.” In fact the founders were not unaware of the Roman Republic and what had happned to it.
Actually:
1. It proves that the word was used, so your claim that it was not is false.
2. The Supreme Court says that “citizen” and “Subject” mean exactly the same thing.
So, your point here appears to be well, pointless.