I've often wondered about this myself because of the way I was passed around by them once I had opened a channel to these spirits. You call on any of them and others will begin to contact you, by and by. So, just from my own experience of them, I would say they are seventy-two facets of a single emanation of the pleroma, in the gnostic sense, though not necessarily deities in their own right., Bael, Astaroth and a few others excepted, which is not to say that Astaroth and Astarte are identical, any more so than Mars is identical to its higher octave, Pluto. If I wanted a demonic contact I would opt for evocation, not otherwise.
I only ever invoke, but then again, I do not treat the grimoires as anything other than grammars either, the prayers and imprecations and what not pertaining to myself; to my inner stance as an operator; to my alignment. They are implicit. So when I work with the daemons I am engaging the alchemical component of theurgy, and in this they excel, as meaning is extracted from the matter of the Sarx which we mistake for the real.
So, when I call upon Astarte I am calling on something higher up in the great chain of being -- something closer to the undifferentiated. And in blessing Astaroth by the power of Asherah/Astarte I initiate reciprocal evolution. Grok? If you look at the explicit metaphysics of grimoire magick as topology the distinctions between demon/angel/deity collapse because really, when you are actually doing the work theory is praxis. Let the work reveal the metaphysics instead of applying the metaphysics to the work.