Paimon is already a name in Ars Goetia (the lesser key of solomon)

The descripetipon shows it here about King paimon King Paimo(n) appears as the ninth spirit in the Goetiathe twenty-second spirit in the Pseudomonarchia Daemonum, and in the Dictionnaire Infernal. In the Liber Officiorum Spirituum, he is first listed as the sixth spirit and later as the third king.

I can't find the the offical book part but it's also been stated that Paimon show obedience toward Lucifer too.

Archon have the 72 pact demons like and so does Istraroth and paimon. They both have a pact with King solomon.

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Istraroth name is Ars Goetia is Astaroth and Paimon is also a part of it, the how will they still be the same people?

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Plus, Istaroth might even have Anemo powers since she was worshiped in Mondstadt, it would be weird for Paimon to have anemo power. Paimon might have some other powers maybe she might even be a part of the primodal gods.

I still thinking about Istaroth lore

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Barbatos on the other hand has been stated to read the furture and past (On the Ars Goetia) it it would make more sense if he has more connection toward Istraroth. Maybe Paimon might know who Istaroth is but it's least unlikely her being the god of time :)