Are you being intentionally ignorant?
We are discussing here the meaning of an adjective. The OED (You should look at it sometime in a library, if you ever go.) is a history of the English language and so gives examples of when specific usage of words and phrases entered the language. In order to show how an adjective is used, you kinda have to use nouns. (Like, duh.) The relevant usage examples of natural-born and native-born entered the language as modifiers of the noun subject.
ML/NJ
Of course they did, because there were no English citizens at that time, only subjects. But that does not mean that "natural born citizens" have the same requirments relative to birth in the country or outside it to other natural born citizens, as "natural born subjects" had. Changing the one word changes the meaning of the "term of art". In English or French. The representatives of the French Monarchy wrote "sujects naturels" in that treaty of commerce with the fledgling US (in conjunction with French speaking US diplomats, most likely Ben Franklin himself, who was at the time the US ambassador to France), while Vattel wrote "naturels" while writing of "cityons" and did so earlier than that treaty was written.
I've been going to libraries since oh about 1958 or so, maybe a little longer. There was a nice, if small, Carnegie library a block from my elementary school. My wife is a college professor, and the school where she is a department chair has a very nice library, much larger than a school their size would normally have. Don't go so much anymore, since most of what I want to know I can look up on line. I do recall going through two different collections of Thomas Jefferson's papers in their "stacks", trying to verify a quote, which is most likely a bogus one.
The (not for profit) research institute I work for has a pretty large library. The US Army command where I'm currently assigned also has a small library. Neither have just technical materials though I doubt the latter has the OED though, the former might.
So yes, I am familiar with libraries. Just a wee bit.