"It was originally proposed in the Constitutional Convention that the presidential qualifications be a 'citizen of the United States.' It was so reported to the Convention, by theCommittee which had it in charge, on the 22nd day of August, 1787. It was again referred to aCommittee, and the qualification clause was changed to read 'natural born citizen,'and was so reported out of Committee on September the 4th, 1787, and adopted in the Constitution."
Madison's notes for the two dates (August 22, September 4) seem to confirm Long's account. It seems strange that he never mentioned Vattel in the account.
I'd say you know more about this issue than Long did. ;-)
It is a fallacy to conclude that the failure to mention something is the equivalent of rejecting it. In looking up the link for the Breckenridge Long article, I happened across some commentary on it.
The commentary noted that Breckenridge Long had failed to mention Minor v Happersett, and therefore the Minor v Happersett case is irrelevant or trivial or something.
As I was reading through the article, I thought to myself, whoever wrote this has less reasoning skills than a monkey with their hand caught in a jar. I looked up the author's name. It was "Squeeke Frome", one of the silliest people i've ever encountered on Free Republic. (Now banned, and for good reason. She was a crackpot of the first order. )
The point is, you can't read too much in the absence of information. A failure to mention something does not preclude it's involvement.
As I mentioned before regarding language, the important aspect is the principle involved, not the language or in this case, the name of the guy who first thought of it. (Actually, Aristotle beat Vattel by thousands of years.)
Several other court cases use the Vattel definition but do not reference the name Vattel, or "law of nations." If it was regarded as American Common law (and Breckenridge Long seemed to think it was) then he didn't need to note it's origin.
Breckenridge Long asserts the citizenship principle of Vattel, whether he mentions the name or not.