We're told that Tuor was allowed in Valinor and was supposedly given immortality (within Arda). Now, after Glorfindel died in the fall of Gondolin, went to Mandos and was re-embodied after a "short time", he must have been in Valinor (outside the Halls of Mandos) for quite some time before he was sent back to ME (in SA 1600?). If this is all true, he would have had ample opportunity to meet Tuor, wouldn't he? And after Glorfindel returned to ME, he could have confirmed to the elfs and to the men that the grandfather of Elrond and Elros walked the streets of Tirion, couldn't he?
The published Silmarillion was edited together (by Christopher Tolkien) from different versions written by J. R. R. Tolkien over something like a 40-50 year span.
The decision to make Glorfindel of Gondolin the same person as the Glorfindel in LOTR was very late in JRRT's life (see "Last Writings" in The Peoples of Middle-Earth [History of Middle-Earth vol. XII]), and so any implications of that decision aren't likely to have been carried through into the Silmarillion stories.
There are other cases like this -- the published Silmarillion goes with the 'Orcs as corrupted Elves' origin although Tolkien later leaned towards Orcs being largely derived from Men (see the Orcs essays in "Myths Transformed" in Morgoth's Ring [HOME vol. X]).