Common Salt is sodium chloride, NaCl, an identification that was never in doubt since the substance under discussion is, and always was, the same familiar salt used at table, requiring no historical detective work to resolve. What does require care is keeping this ordinary mineral salt distinct from the alchemical principle Salt, one of Paracelsus's tria prima alongside Sulphur and Mercury, which named an abstract quality, fixity and incombustibility, the ash that remains after a body is burned, rather than any single chemical compound.
The alchemical principle Salt is traditionally associated with earth and Saturn as a philosophical category, not with sodium or chlorine or any specific mineral, and conflating the two, treating table salt as if it carried the metaphysical weight of the Paracelsian principle, is exactly the kind of category error historians of alchemy warn against. Common salt earns its place in a survey of chemical substances precisely because it is the plain, everyday case against which the more exotic and more contested named salts and vitriols can be measured. Its very ordinariness is part of the point of including it here: a table built only from dramatic, contested or toxic named substances would give a misleading picture of the plain, everyday chemical materials alchemists actually kept close at hand.