In the so called "book of hagoth", it says that the people of hagoth or the "Nemenhah" keep in contact with the other Nephites, that the Nephites traded with the Nemenhah, that Shiblon sent word to the Nemenhah, that Helaman sent teachers to the Nemenhah, and that Nephi the son of Helaman even came and spent some time among the Nemenhah.
But in The Book of Mormon; Alma 63:5-8, it clearly says:
5 And it came to pass that Hagoth, he being an aexceedingly curious man, therefore he went forth and built him an exceedingly large ship, on the borders of the land bBountiful, by the land Desolation, and launched it forth into the west sea, by the cnarrow neck which led into the land northward.
6 And behold, there were many of the Nephites who did enter therein and did sail forth with much provisions, and also many women and children; and they took their course northward. And thus ended the thirty and seventh year.
7 And in the thirty and eighth year, this man built aother ships. And the first ship did also return, and many more people did enter into it; and they also took much provisions, and set out again to the land northward.
8 And it came to pass that they were never heard of more. And we suppose that they were drowned in the depths of the sea. And it came to pass that one other ship also did sail forth; and whither she did go we know not.
Now read verse 8 again.
Ok, so I would say that this so called "book of hagoth" is a hoax.