They WERE interchangeable and synonymous. Over time, the meanings diverged. The meaning of the word "native" has undergone a transformation from what it meant back in 1787.
Schneider v. Rusk (1964):
“We start from the premise that the rights of citizenship of the native born and of the naturalized person are of the same dignity and are coextensive. The only difference drawn by the Constitution is that only the ‘ natural born’ citizen is eligible to be President. Art. II, s 1.”
This is a modern meaning which has been crippled by the incorrectly expanded precedent of Wong Kim Ark. Before people's misunderstanding of Wong Kim Ark became common place in most legal minds, the meaning of the word "native" was very clearly synonymous with "natural born."
WAITE, C.J., Opinion of the Court
SUPREME COURT OF THE UNITED STATES
88 U.S. 162
Minor v. Happersett
Argued: February 9, 1875 --- Decided: March 29, 1875
The Constitution does not, in words, say who shall be natural-born citizens. Resort must be had elsewhere to ascertain that. (Bye Bye 14th Amendment!) At common-law, with the nomenclature of which the framers of the Constitution were familiar, it was never doubted that all children born in a country of parents who were its citizens became themselves, upon their birth, citizens also. These were natives, or natural-born citizens, as distinguished from aliens or foreigners.
As you can see from the superior authority I cited, the word "native" did not mean what you take it to mean nowadays. Modern Usage of the word has simply been transformed from it's original meaning.
I agree with you that times change and meanings change. If your side can find any judicial opinion or any congressional action to support separating native born from natural born here in 2013, I’ll be impressed. Until then, not so much.