Did the 🧝elves not know Gil Galad's fate?

[Idril Celebrindal]

Gil Galad died during the sige of Barad-Dur. Isildur himself recorded his death. An yet part of the song that Sam sings near Amon Hen makes it seem as if his fate is unknown.
"But long ago he rode away
And where he dwelleth none can say
Far into darkness fell his star
In Mordor where the shadows are"
The "And where he dwelleth none can say" part makes is seem as if the elves really didn't know what happened to Gil Galad, or that they thought he was taken captive by Sauron. But wouldn't his death have been seen by many? And you would think that Isildur would tell peope what happened to Gil Galad, if nobody else saw it. So did Bilbo make a mistake while translating the song from Elvish (Sindarin, I'm assuming?)? Or is the "Where he dwelleth none can say" somehow connected with the choice of Elves to come back to Arda after they die, and the Elves are wondering if he was reborn or not? Or is this simply a small mistake made by Tolkien, however unlikely that may seem?
Or am I misinterpreting the song?

 

[Eljorahir]

But wouldn't his death have been seen by many?

At the Council, Elrond even provides his eyewitness account:
'...I beheld the last combat on the slopes of Orodruin, where Gil-galad died, and Elendil fell, and Narsil broke beneath him; but Sauron himself was overthrown...'

"Where he dwelleth none can say"

Within the pages of The Lord of the Rings, I think there is no mention of Mandos nor his Halls. The "where he dwelleth none can say" line suggests that the poet had a sense that Gil-galad's spirit lives beyond his bodily death, but he doesn't know where it resides.

Then again, maybe someone else will have a better idea.

 

[Radaghast]

I think that's right, @Eljorahir. The line says "where he dwelleth" implying perhaps that he's been resurrected somewhere, but it's fairly clear on where he died if not how, suggesting it's common knowledge (relatively speaking).