Seven: Four From Five or One?

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Appendix B, The Tale of Years, of The Return of the King, gives us a hint regarding when the Dragons may have consumed the four Rings of Power.

The Third Age: Year 2570 - About this time Dragons reappear in the far north and begin to afflict the Dwarves.

and

Year 2589 - Dáin I is slain by a Dragon.

At this time Sauron's already in Dol Guldur, Sméagol-Gollum is in hiding with the One Ring in the Misties, Brego's built the Golden Hall, Elrond's widowed (no, she didn't die, but he has the remote all to himself), Thrór and his Ring return to Erebor and his brother, Grór heads off to the Iron hills (and whats does he have in his pocketses?).

So, to me, with the fall of Dáin, we know the fate of one. Three to go...