There was silence. At last Elrond spoke again. [...] The Barrow-wights we know by many names; and of the Old Forest many tales have been told: all that now remains is but an outlier of its northern march. Time was when a squirrel could go from tree to tree from what is now the Shire to Dunland west of Isengard. In those lands I journeyed once, and many things wild and strange I knew. But I had forgotten Bombadil, if indeed this is still the same that walked the woods and hills long ago, and even then was older than the old. That was not then his name. Iarwain Ben-adar we called him, oldest and fatherless. But many another name he has since been given by other folk: Forn by the Dwarves, Orald by Northern Men, and other names beside. He is a strange creature, but maybe I should have summoned him to our Council.'
> In those lands I journeyed once, and many things wild and strange I knew. But I had forgotten Bombadil, if indeed this is still the same that walked the woods and hills long ago, and even then was older than the old. That was not then his name.
My takeaway from this was that Elrond wasn't sure if this was the same person - strongly speculated to be, and probably correct, but not someone Elrond had personally known or corresponded with. It felt like this was the first time he'd heard the name Tom Bombadil, and made an educated guess that it was probably old Ben-adar. Tom, meanwhile, had contact with Gildor at the very least.
