Sovereignty can be tested by violations of interests that we categorically refer to as Property in Toto. A man is sovereign or he is not. He can demonstrate reciprocity in sovereignty or the cannot.
Individualism, like non aggression, is just a weasel word for not defining the scope of interests against which one cannot impose costs, and the institutional means by which such a condition is created and preserved, against competition from those with different intentions.
Sovereignty is an empirically testable definition. Individualism is just a means of weaseling out of a testable definition and thereby preserving means of deception.