The Lost Road and other writings tell us : "Yet not all the Eldalië were willing to forsake the Hither Lands where they had long suffered and long dwelt; and some lingered many an age in the West and North, and especially in the western isles and in the Land of Leithien. And among these were Maglor, as hath been told; and with him for a while was Elrond Halfelven, who chose, as was granted to him, to be among the Elf-kindred; but Elros his brother chose to abide with Men."
Let's imagine that at some point during the War of Wrath, for safety's sake, Maedhros and Maglor send Elrond and Elros to Gil Galad... That there, Elros would learn to work with men, and would make his place among them...
How then would Elrond find himself back with Maglor for a time? And how long is a time anyway?
This is my answer.
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