[piosenniel]

Let me chime in here with what Tolkien says about Elrond's rescue party for Eregion. I've already shared this with Envinyatar.

Elrond is chosen to aid the Elvensmiths in 1695. For what ever reasons, it will take the Lindon Elves until 1697 to come near Eregion. Sauron sends his troops against them and they are unable to enter Eregion at all, despite the additional aid they receive from a group of Lorien Elves led by Celeborn. Eregion is destroyed, Ost-in-Edhil in ruins.

Elrond and Celeborn's troops are nearly destroyed by Sauron and company - when King Durin III of Moria sends some Dwarven troops along with another group of Lorien Elves against Sauron's troops from the rear.

Sauron's army turns its focus on the Dwarves and Lorien Elves, driving them back to Moria - the West-gate, which faces Eregion, is then shut tightly against Sauron's troops and none can enter.

Elrond takes advantage of the changed focus of the enemy and with what remains of his men, along with some refugees from Eregion that he picks up along the way, he retreast northeast to the hidden valley where he will establish Imladris.

Sauron, in the meantime, sweeps east over Eriador, heading toward Lindon.

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So ----

- the Elves from Lindon will not enter Ost-in-Edhil and fight alongside the Elvensmiths

- the Dwarves and Elves of Lorien, however, can certainly join in the battle alongside the Elves of Eregion