Mobom.org (Museum of the Book of Mormon) has a discussion of Letter VII here:
When he wrote Letter VII, Oliver Cowdery was Assistant President of the Church. Joseph Smith referred to him as President Cowdery because, as Assistant President, he was a member of the First Presidency and senior to the First and Second Counselors.
Letter VII is President Oliver Cowdery's explanation of not only the fact of the location of the Hill Cumorah described in Mormon 6:6, but also the number of Jaredites and Nephites/Lamanites who died there (far fewer than often assumed). President Cowdery explained that Joseph helped him write these letters.
|Letter VII excerpt (click to enlarge)|