The bottom line: Joseph Smith specifically directed his scribes to incorporate Oliver Cowdery's letters into his (Joseph's) personal history. This includes Letter VII, which unequivocally identifies the New York Cumorah as the scene of the final battles of the Jaredites and Nephites. Note that this predates the 1842 history by seven years.
I bring this up again because Mesoamericanists demand "documentary" proof of such things as Joseph's use of the word "Cumorah" before others used the term. Their entire theory rests on the Book of Mormon Cumorah not being in New York.
The Cowdery letters were published at least three times during Joseph's lifetime, once with his express permission and another time by his brother Don Carlos in the Times and Seasons (in 1841). The letters were in the very same book that contained the "History of Joseph Smith" published in serial form in 1842, when Joseph was the nominal editor of the Times and Seasons. Joseph or his scribes always maintained possession of this book. Joseph invoked Cumorah in the Sept. 1842 letter that became D&C 128. What more could he have done to demonstrate that he approved of what Cowdery had written?
The Mesoamericanists could argue that Joseph should have published Letter VII while he was editor, but it had already been published in the Times and Seasons just a year earlier. How many republications would it have taken to satisfy today's Mesoamericanists?
Because of their dogmatic insistence on a Mesoamerican setting, the Mesoamericanists reject this history and cling to the anonymous articles in the Times and Seasons that were never referred to again after they were first published. (I think the evidence demonstrates they were an agenda-driven mistake, published by William Smith, who was fired as a result, and written by Benjamin Winchester, edited by W.W. Phelps and William.) Even the Mesoamericanists admit the articles were factually inaccurate, but they continue to insist on tying them to Joseph Smith because without those articles, there is zero foundation for a Mesoamerican setting for the Book of Mormon.
Lately, I've been referring a lot of people to the Joseph Smith Papers. You can go here for an overall directory. For an overview of his journals, go here. For an overview of his histories, go here. These may appear intimidating at first, but the commentaries are excellent and the papers accurately show what happened, as opposed to the compilations in History of the Church.
Joseph Smith was not a prolific or accomplished writer, which is why he had so many scribes working for him throughout his life (and why the revelations in D&C are so miraculous). Theoretically, he could have translated the Book of Mormon without a scribe. But as is well known, he lacked much formal education and he had time pressures throughout his life. As Wilford Woodruff noted in June 1842 (when Mesoamericanists insist Joseph was writing editorials and actively editing the Times and Seasons), Joseph "hardly gets time to sign his name."
Even though Joseph recognized the need to record history, he had trouble getting it done. (Even in our day, how easy is it to maintain a journal?)
Joseph Smith started his first history in 1832, but it was only 6 pages long and was written partly by him and partly by Frederick G. Williams. The JSP Historical Introduction explains: "It is not clear why JS ended his earliest history before completing his stated intentions. Some of his other documentary endeavors, including the journal he began the same year, are similarly incomplete, perhaps indicating that other activities simply took precedence.1 It is possible, however, that JS deliberately ended the history where he did, viewing it as part of a larger historical record that would include the work of others assigned as record keepers. Even though JS wrote his own history in about summer 1832, he continued to affirm John Whitmer’s role as church historian, demonstrating that JS’s historical venture did not relieve Whitmer of the responsibility to continue the church history. For his part, Whitmer viewed his history as continuing work begun by Oliver Cowdery, whom he replaced as church record keeper. The question of whether JS expected Cowdery’s or Whitmer’s work to fit together with the account begun in his own history cannot be settled for certain; JS’s narrative does, however, cover only earlier history for which JS alone could provide a firsthand account, and it concludes just before Cowdery enters the scene."
Joseph started his first journal later that year. The JSP Historical Introduction explains: "JS’s first journal begins 27 November 1832 and ends 5 December 1834, with entries spread unevenly over this period of just over two years. After titling this journal “Joseph Smith Jrs Book for Record,” JS recorded his ambitious intention “to keep a minute acount of all things that come under my obsevation &c.” However, reality failed to match his expectations. From the outset, the level of detail JS preserved in this record was limited. His pattern of journalizing varied widely. After recording only nine more entries, JS abandoned journal keeping for ten months. Yet his original aspiration to keep a journal occasionally yielded significant information. Sporadic notations followed, with three instances of sustained writing covering a consecutive week or more in the remainder of the journal."
The second history (History, 1834-1836), which you can read here, incorporates the Cowdery letters.
I'm going to enter the citation cartel in one final attempt to persuade the Mesoamericanists on this issue. None other than Jack Welch pointed out how integral Cowdery's letters were to Joseph's own history. (I pointed out previously that Welch omitted any discussion of Cumorah, but keep Letter VII in mind when you read this passage from his chapter, "Oliver Cowdery as Editor, Defender, and Justice of the Peace in Kirtland," pp. 262-4, in Days Never To Be Forgotten: Oliver Cowdery.) I'm omitting footnotes but bolding important points. I can't tell whether Welch realized at the time that Joseph had incorporated these letters into his history, but that endorsement by Joseph is even more significant, IMO, than his helping Cowdery write the letters in the first place.
The history of the Church was a leitmotif in the Messenger and Advocate under Oliver Cowdery's supervision. He made this explicit in the first issue when he wrote that he would be including history of the events in New York and Pennsylvania to which he was privileged. He wrote, "We have thought that a full history of the rise of the church of hte Latter Day Saints, and the most interesting parts of its progress, to the present time, would be worthy the perusal of the Saints.--If circumstances admit, an article on this subject will appear in each subsequent No. of the Messenger and Advocate, until the time when the church was driven from Jackson Co. Mo. by a lawless banditti."
Soon thereafter, John Whitmer was called to replace Cowdery as the official Church historian. Nevertheless, Cowdery continued to act as a historian. He was the only person other than Joseph Smith with firsthand knowledge of many of the founding events of the Restoration. Thus, it was only natural for him to write columns about the history of the Palmyra period of the Church.
Joseph Smith fully supported Cowdery's efforts to publish his history and even offered to assist him with it. Cowdery said that Joseph Smith's labor on the project and "authentic documents now in our possession" would give him the ability to write a historical narrative that was "pleasing and agreeable" to his readers. Would that we had all the documents Cowdery was working from, as documents from the early years of the Church are so rare.
Oliver Cowdery included several serials in the form of letters originally sent to W.W. Phelps in Missouri describing the early spiritual experiences of Joseph Smith. Taken together, they constitute one of the earliest recorded histories of the Palmyra period. He was not able to cover the swath of history he had hoped (from the First Vision to the expulsion from Jackson County), but he was able to cover from the First Vision to the restoration of the Aaronic Priesthood. Cowdery's history is invaluable because it contains details that are unique to it, and it is much more detailed than those accounts left by the Prophet himself. But because Cowdery writes that Joseph assisted him with the writing of this history, the division between Cowdery's and Joseph's versions may be a false construct. Either way, the following is a sampling of some of the unique insights provided in Cowdery's Messenger and Advocate letters.