Is there an in-universe explanation of how Frodo's arrival in Valinor was recorded in the Red Book?

Question

In the chapter "The Grey Havens", we have:

And the ship went out into the High Sea and passed on into the West, until at last on a night of rain Frodo smelled a sweet fragrance on the air and heard the sound of singing that came over the water. And then it seemed to him that as in his dream in the house of Bombadil, the grey rain-curtain turned all to silver glass and was rolled back, and he beheld white shores and beyond them a far green country under a swift sunrise.

So I was wondering whether this scene could have been recorded in the Red Book (or any other record of Middle-earth), since I am not aware of any people or information travel from Valinor back to Middle-earth after the end of the Third Age.

Answer 1

It is possible that Frodo's arrival in Valinor is an accurate recording of factual events in-universe

While, as far as we understand, there are no more immigrants from Valinor (only those heading to Valinor) who could bear tale of Frodo's arrival, there is at least one way for this to be an accurate factual account in Middle Earth.

Aragorn, who at the start of the Fourth Age possesses a palantír, both loved Frodo (friend, companion, hero), Bilbo (old friend), Gandalf (old friend, advisor, leader), Elrond (father in-law, father-like figure), and Galadriel (grandmother in-law, revered Noldo), and had motivation, values, capacity, and right to see visions of the undying lands, may have watched from afar as the ship from the Havens passed into the West. (In Unfinished Tales a note describes one of the stones as being specifically 'oriented' so that it always gazed to "Eressëa in the vanished West," implying that other stones might be directed that way also.) So the end of Frodo's journey may thus actually have been recorded as an in-universe fact which was subsequently passed along to the remaining hobbit members of the Fellowship, for example, when King Elessar visited the Shire, as recorded in the Appendices in Return of the King.

Answer 2

The book does not claim to have recorded this. Before leaving, Frodo gives the book to Sam, inviting him to write the ending -

"I have quite finished, Sam," said Frodo. "The last pages are for you." - Book 6, Ch 9, The Grey Havens

I think we can assume that the ending was written not as a witnessed record, but rather the way Sam — who loved Frodo and legends — believed Frodo's story should end.

Answer 3

It’s not eyewitness testimony, it's a literary flourish

The most likely perpetrators of this are either Samwise Gamgee, its original author, or J.R.R. Tolkien its translator into English. However, it is possible that this flourish was added during the transcription from the Red Book to the Thain's book or in the final transcription back to the manuscript stored in Great Smials that served as Tolkien's reference. If anyone has access to this manuscript and can speak Westron (I can't), they will be able to tell you if the flourish is in that document.

I lean towards Tolkien; it has been argued¹ that Tolkien's translations of Beowulf were a work of metafiction rather than a mechanical translation (insofar as anything beyond Google translate can be a mechanical translation). In the case of both the Red Book and Beowulf, while both purport to be a history of real events, from this distance both are legendary which is to say it impossible to determine how much if any is factual and how much is the author recording myth and legend as fact.²

¹Vladimir Brljak. "The Books of Lost Tales: Tolkien as Metafictionist." Tolkien Studies 7 (2010): 1-34. https://doi.org/10.1353/tks.0.0079 (accessed September 23, 2019).

²Yes, I know that the LotR is Tolkien's original work but it's more fun to pretend it isn't just like Tolkien did.

Answer 4

In The Fellowship of the Ring, Book I, Chapter 8, "Fog on the Barrow Downs" the night that the hobbits spend in the house of Tom Bombadil before leaving to cross the Barrow Downs is briefly described:

That night they heard no noises. But either in his dreams or out of them, he could not tell which, Frodo heard a sweet singing running in his mind: a song that seemed to come like a pale light behind a grey rain-curtain, and growing stronger to turn the veil all to glass and silver, until at last it was rolled back, and a far green country opened before him under a swift sunrise.

The vision melted into waking; and there was Tom whistling like a tree full of birds; and the sun was already slanting down the hill and through the open window. Outside everything was green and pale gold.

And presumably this was recorded by Frodo writing the story of his journey. And Sam would have read about that vision. And possibly Sam came to the conclusion that Frodo's vision was prophetic, and so later wrote:

And the ship went out into the High Sea and passed on into the West, until at last on a night of rain Frodo smelled a sweet fragrance on the air and heard the sound of singing that came over the water. And then it seemed to him that as in his dream in the house of Bombadil, the grey rain-curtain turned all to silver glass and was rolled back, and he beheld white shores and beyond them a far green country under a swift sunrise.

Sam certainly hoped that was how the journey ended. He certainly wasn't going to write that when they came in sight of the Lonely Island a voice of thunder from the sky said: "So, you dare to bring a mortal to the Undying Lands! Take this!" and then the ship was struck by lightening and exploded.

And it is possible that Sam also had a vision of Frodo's arrival before or after the fact.

Added 09-25-19. Eugene Styer's answer mentions another experience of Frodo's which Frodo should have written down in the Red Book - how else would the modern translator Tolkien ever learn about it - and which could have influenced Sam to write the ending of Frodo's voyage the way he did.

Answer 5

I know i'm answering my own question, but I was thinking about it, and an idea came to me that would fit nicely - The Mirror of Galadriel. While looking in the mirror, Frodo saw

... the sun went down in a burning red that faded into a grey mist; and into the mist a small ship passed away, twinkling with lights. It vanished, ...

He wouldn't have understood it at the time, but while planning to leave or travelling to the Havens he could have written about arriving in Valinor based on what he saw in the mirror before leaving Middle-Earth, possibly combined with information from Bilbo's translations and elves (such as Galadriel) who had been in Valinor in the past.