> The ex post facto provision is normally interpreted to apply only to criminal laws, not to civil penalties or taxes.
FWIW, the precedent distinguishing prohibited ex post facto laws from permitted retrospective laws was established by the Supreme Court when ink on the Constitution was practically still wet, in Calder v. Bull (1798).
It has also been rolled back. I do not remember the specific case, but it dealt with the SOR requirements being extended on people long after they has been convicted and sentenced due to a change in SOR laws. The courts ruled that it did not violate ex post facto. If that doesn't violate it, then taxes definitely wouldn't either.
I think there is an applicable quote about defending scoundrels that would apply here.
An interesting side note is that many state courts have continued to strike down similar provisions, and some Federal courts have apparently also concluded that certain rules about sex offenders are "punitive" and so constitutionally invalid as outside of the Smith v. Doe rule. So this example is hard to summarize in a simple way, not least because many other courts have been trying to narrow this rule.
FWIW, the precedent distinguishing prohibited ex post facto laws from permitted retrospective laws was established by the Supreme Court when ink on the Constitution was practically still wet, in Calder v. Bull (1798).