Jerry Ainsworth notes that in Ether 4:4, Moroni says "I have written upon these plates the very things which the brother of Jared saw" (emphasis added). In other words, he has written the brother of Jared's vision on the identical plates upon which he's continuing to write, not on later plates. [Jerry L. Ainsworth, The Lives and Travels of Mormon and Moroni, p. 217]
“The Very Things Which the Brother of Jared Saw”
According to Jerry Ainsworth, it appears that the language (or the symbols) that the brother of Jared and the prophet Ether used for writing upon plates actually caused events to be "shown" to the reader. A person using the Urim and Thummim in order to obtain the information would therefore see the events inscribed on the plates. Perhaps that is why people who have the ability to access the events of ancient records are called "seers." Using an abbreviated form of writing--a set of codes--a seer writing upon plates would in that case not be required to write a description of each event. He would simply write the symbols that caused the Urim and Thummim to show their user the events themselves. That might explain why Moroni wrote what he did "according to my memory" (Ether 5:1), not according to a verbatim account. Moroni himself saw the events, both those in the past and in the future. In other words, Moroni wrote down "the very things which the brother of Jared saw" (Ether 4:4), not necessarily the things the brother of Jared had written. Moroni saw what the brother of Jared had seen. [Jerry L. Ainsworth, The Lives and Travels of Mormon and Moroni, p. 215] [See the commentary on 2 Nephi 27:7; Ether 1:4]