I am waiting for Finland and/or Denmark to announce that any vessel not passing inspection by one of the Classification Societies that is part of the the International Association of Classification Societies is subject to boarding, inspection, and impoundment if it cannot pass an inspection by their Coast Guard. For the safety of their shores, national waters, and underwater infrastructure.
If you've ever been out on the water, seen a freighter and wondered how they decided where the load line (how deep the hull can sit in the water) on the hull comes from - it's out of a classification society. Classification is not the same thing as insurance, although not having the first makes the second more expensive or unavailable.
https://en.wikipedia.org/wiki/Ship_classification_society
I think I can safely say that the RF's shadow fleet has zero vessels 'in classification' with the IACS.
UNCLOS II says nothing about classification being necessary for the 'right of innocent passage', but nations have the right to suspend or condition IP.
Without getting into whether allowing the shadow fleet for the last couple of years has been a deliberate policy by the West. I think it has been, but this comment is long enough...