[Formendacil]

Fact: Sauron gave seven Rings of Power to Dwarf-kings.

Fact: There were seven ancestral houses of Dwarves.

Only Speculation: The seven "Dwarf-lords in their halls of stone" who received the seven Rings corresponded one-to-one to the seven different Dwarf-tribes.



Fact: By the time of the Rings' forging, at least one Dwarf-house (Nogrod) and possibly two (Belegost) were greatly weakened.

(Related question: from simple geography, how likely is it that Sauron, in the years after the destruction of Eregion and the theft of the the work of the Mirdain, went anywhere near the Blue Mountains, so close to Lindon?)

Fact: Dwarves in the Second Age could have more than one kingdom--or, at least, more than one outpost. The Longbeards ruled the Misty Mountains from Moria to Gundabad, and across the Grey Mountains, with an outpost colony in the Iron Hills. Who is to say that the four Dwarf-tribes of the East did not have multiple kingdoms? In the earlier Ages of their greatest fecundity, why couldn't the Dwarves had spread to found more than seven ancestral houses?

We know, at the very least, that the Rings of Power given to the "kings of Men" could not have all gone to literal Kings, because three of them went to Númenóreans, none of whom were Kings of Númenor. The possibility for a similar sort of analogy seems to me to be at least potentially in play here.