As you have found, Peter, variations are a continuum and also are not necessarily genetic. Many are described as 'pathological', meaning they are due to disease of some sort.
Naming aberrations became a Victorian passion and the entomologist J.W.Tutt named loads of them; many of his names overlap with others and there are no 'definitive' versions.
Remember, as someone else pointed out, that all this 'naming' is a purely human invention. Speciation is a human invention, too, and hence there are frequent changes in the groupings over time. DNA analysis has added a new twist to all this, and shown that morphological features are often a poor guide to the way evolution has progressed.
In summary, evolution is a continuum, where
all the boundaries are human inventions. They are a convenience, helping us to describe and understand the living world
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