Okay then I was wrong about an amendment being required for the NST. 'preciate the info.
So the fix in the sixteenth was unnecessary.
That's what the Supreme Court recognised in:
Stanton v. Baltic Mining Co.(1916), 240 U.S. 103:
The 16th was more a restriction on the Courts ability to "interpret" the taxing clauses of the Constitution than is was a change in the inherent power of Congress to lay and collect taxes. The power to lay and collect the "income" tax was recognized long before the 16th, especially as it concerned individuals in commercial relationships with others.