Good point, here. It is written (somewhere - sorry!) that Durin's House were the only Dwarves that had contact with the Elves, and that none of the other Houses come into any of the tales. But if that is so, then why did Celebrimbor (or whoever actually gave them) give a Ring of Power to these other 6 Houses that he never had any dealings with?
Perhaps Sauron, as Annatar, travelled to the other Dwarf realms to dole them out and attempt to control other Dwarf Houses. The only other explanation could be that all Seven went to Dwarves of Durin's House. The Messenger of Mordor described by Gloin (
The Council of Elrond, Book II) talks about Sauron rewarding Dain with
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rings, such as he gave in the past
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We know that four were consumed by dragons, and three were recovered by Sauron - one from Thrain in Dol Guldur. Were the other two taken by Goblins in one of the many battles of the Goblin Wars, to be recovered by Nazgul later?
By the way, Bombadil, two Elf rings were given to Gil-Galad and one to Galadriel - not very systematic.