How come the writers of the small plates followed meticulously the instructions of Nephi?

It is interesting how some of the writers of the small plates have little to contribute to the Book of Mormon, for example Chemish only writes one verse in Omni 1:9:

Now I, Chemish, write what few things I write, in the same book with my brother; for behold, I saw the last which he wrote, that he wrote it with his own hand; and he wrote it in the day that he delivered them unto me. And after this manner we keep the records, for it is according to the commandments of our fathers. And I make an end.

Why would multiple authors only contribute a few verses or very little in quick succession? John W.Welch notes how this follows instructions given by Nephi in Jacob 1:1-4

1 For behold, it came to pass that fifty and five years had passed away from the time that Lehi left Jerusalem; wherefore, Nephi gave me, Jacob, a commandment concerning the small plates, upon which these things are engraven.
2 And he gave me, Jacob, a commandment that I should write upon these plates a few of the things which I considered to be most precious; that I should not touch, save it were lightly, concerning the history of this people which are called the people of Nephi.
3 For he said that the history of his people should be engraven upon his other plates, and that I should preserve these plates and hand them down unto my seed, from generation to generation.
4 And if there were preaching which was sacred, or revelation which was great, or prophesying, that I should engraven the heads of them upon these plates, and touch upon them as much as it were possible, for Christ’s sake, and for the sake of our people. (emphasis added)

This explains why Abinadom would say in Omni 1:11

And behold, the record of this people is engraven upon plates which is had by the kings, according to the generations; and I know of no revelation save that which has been written, neither prophecy; wherefore, that which is sufficient is written. And I make an end. (emphasis added)

How would Joseph Smith manage to be consistent like this if he was dictating the Book of Mormon on the fly?

See:

Evidence Central – Book of Mormon Evidence: A Pattern in the Small Plates

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