John W. Welch describes the year rite as follows:
The ancient Near Eastern year rite festival was an annual event at which the king called his people together, gave an accounting of his actions, placed the people again under obligation to abide by the law, prophesied, acclaimed all men equals, proclaimed them the children of God, and recorded their names in the registry of life. Such elements of the typical ancient year rite are readily discernible in several Book of Mormon assemblies, particularly that of King Benjamin in chapters 2 through 6 of the book of Mosiah.– John W. Welch – Hugh Nibley and the Book of Mormon
Of all the Book of Mormon evidences, Hugh Nibley singled out the year rite in Mosiah as the strongest.
In the writer’s opinion,…the most convincing evidence yet brought forth for the authenticity of the Book of Mormon [is the matter of the year-rite]. Very likely the reader will be far from sharing this view, since the force of the evidence is cumulative and is based on extensive comparative studies which cannot be fully presented here. Still the evidence is so good, and can be so thoroughly tested, that we present it here for the benefit of the reader who wishes to pursue the subject further. Since Gressmann, Jeremias, Mowinckel, and many others began their studies at the start of the century, a vast literature on the subject of the Great Assembly at the New Year and the peculiar and complex rites performed on that occasion has been brought forth. Yet nowhere can one find a fuller description of that institution and its rites than in the Book of Mormon. Since “patternism” (as the awareness of a single universal pattern for all ancient year-rites is now being called) is a discovery of the past thirty years, the fact that the now familiar pattern of ritual turns up in a book first published in 1830 is an extremely stimulating one. For it is plain that Mosiah’s account of the Great Year Rite among the Nephites is accurate in every detail, as can be checked by other year-rites throughout the world….– Hugh W. Nibley, An Approach to the Book of Mormon, 3rd edition, (Vol. 6 of the Collected Works of Hugh Nibley), edited by John W. Welch, (Salt Lake City, Utah : Deseret Book Company ; Provo, Utah : Foundation for Ancient Research and Mormon Studies, 1988), Chapter 2
How would Joseph Smith know anything about the year rite or be able to describe it so accurately in every detail?