Historical analysis: It is interesting that Nephi records his explicit instructions for the line of transmission of the large plates, but neglects to indicate any transmission line for the small plates. We know that the small plates proceed among family (not always father to son, as Nephi gives them to his brother Jacob) but the large plates appear to have a more specific transmission that has been agreed upon by the people (another aspect conspicuously absent from the transmission line of the small plates).
The large plates are specifically to be handed down from generation to generation. Nephi assumes that they will go from prophet to prophet, though that concept of transmission is obviously transcended in later practice, and the large plates stay with the ruler and follow the same transmission line as the political rulership. Perhaps Nephi, being both prophet and leader assumed that the two roles would remain intertwined. That was not the case in Nephite history at all times. Nevertheless, the transmission of the large plates appears to be consistent with the changing of the authority to rule, coming back into the hands of the prophets late in Book of Mormon history.
With this dual transmission line and plates with differing purposes, it is not surprising that they eventually become separated, such that Mormon is apparently unaware of the small plates until he comes across them in the course of his abridgement (Words of Mormon 1:3 And now, I speak somewhat concerning that which I have written; for after I had made an abridgment from the plates of Nephi, down to the reign of this king Benjamin, of whom Amaleki spake, I searched among the records which had been delivered into my hands, and I found these plates, which contained this small account of the prophets, from Jacob down to the reign of this king Benjamin, and also many of the words of Nephi).