Yes, that’s exactly my point.
That is what makes the timeline GGP laid out impossible:
> We can pass a wealth tax tomorrow and it’ll suddenly be taxable.
Unless we don’t share a common definition of “tomorrow” or “suddenly”. (For reference, the 16th Amendment process took about 3 years and 7½ months from Senator Norris Brown’s initial formal proposal to ratification by the then-necessary 36th state. [You would need 38 states today.])