And, don't forget, part of Letter I is included in the Pearl of Great Price.
Plus, Letter VII was republished in England in an 1844 pamphlet. It was republished in The Prophet, the Millennial Star, and the Improvement Era.
Amnesia about Letter VII took hold in the early 1900s when scholars began insisting that the "real Cumorah" was in Mexico. Letter VII has never been published in the Ensign. You won't find it in any of the publications by the citation cartel, with the exception of an early first draft of my book which Book of Mormon Central, to their credit, included in their archive, here.
Oliver wrote the letters partly in response to the October 1834 publication of Mormonism Unvailed. I've discussed this before so I won't belabor it. But look at the specific issues Oliver answered in his letters.
1. Location of Cumorah in New York. Oliver explained exactly where the final battles took place: in the valley west of the Hill Cumorah in New York. No need to speculate about other locations or go on search parties to Mexico.
2. Location of Mormon's repository (Mormon 6:6) in the Hill Cumorah in New York. Oliver unambiguously declared the location to be in the same hill where Joseph found the plates. Later, Brigham Young told us about Oliver's personal experiences inside the depository.
3. The numbers of people killed during the final battles at Cumorah; i.e., there were "thousands" of Jaredites killed (less than 10,000) and "tens of thousands" of Nephites and Lamanites. This is far fewer than the numbers usually cited by anti-Mormons and Mesoamerian supporters.
Amnesia about Letter VII has led LDS scholars and educators to speculate and write extensively about these three issues, all oblivious to what Oliver wrote. Or, worse than amnesia, actively disagreeing with Oliver.
Rather than ignore, forget about, or actively oppose what Oliver and Joseph taught through these letters, we should embrace these teachings.