Predating the Interstate Commerce Clause (“ICC”) would not really affect things. I am not aware of a “grandfather clause” exception to the Supremacy Clause. Furthermore, the ICC is older than most states.
Besides what you are actually referring to is not the ICC but the “Dormant” or “Negative Commerece Clause,” which prohibits states from enacting legislation that “unjustifiably . . . discriminates against or burdens the interstate flow of articles of commerce.”
The dormant commerce clause–is actually becoming a fairly interesting topic of debate, as some of the more libertarian Supreme Court Justices are starting to take note that the “Dormant Commerce Clause” is nowhere in the Constitution.
Nonetheless, the Dormant Commerce Clause does exist in practice. The theory supporting it is that, since the Consititution gave the Federal Government the power to regulate interstate commerce, the States cannot abidge this power with its own regulations.
However, the States regulate interstate commerce all of the time–whether it is Iowa saying semis cannot use two trailors, Arizona limiting the length of freight trains, speed limits, highway, rail or air safety, state corporate law, etc. There is probably just as much, if not more, state regulation of interstate commerce as federal.
Such regulation is perfectly permissible. The real concern of the Dormant Commerce Clause is that the States will use their regulatory power to favor their own local industries at the expense of out-of-state industries.
When this is the case, the State regulation/favoritism is struck down unless the State can prove a very important and necessary reason for the regulation. Also, if the State regulation “significantly” hinders interstate commerce, but does not really favor in-State industry to out-of-state industry, the law can still be struck down–but the State does not have as heavy of burden proving the need for the regulation and regulations are rarely s