You know one way to interpret the C rating is to remove ambiguity. If it's not on any of the lists, then it leaves the question of weather a specific species has been considered. If it has a C rating then you know how it's considered from a government perspective. I think when dealing with the government I'd rather have things clearly defined than to leave them to the arbitrary musings of a government official.
Granted
Regulations are designed to retard the spread or to suppress at the discretion of the individual county agricultural commissioner.
Is still a little ambiguous, but less so
It still makes literally no sense to put native species that are already everywhere and not really pests in any way onto it, whike I could name a few seriously invasive species that are not on the list at all.