That's an awesome legacy.
He wrote many articles over the years. One, published in the Improvement Era in 1970, was titled "Confirming Records of Moroni's Coming." In it, Brother Anderson explained the important role President Cowdery's letters play in our understanding of Church history.
You can read his article here:
In the article, Brother Anderson notes this:
"The first published history of the coming of Moroni appeared in letter form in the Messenger and Advocate in 1835. [Note: this is Letter IV.] Its author was Oliver Cowdery, but its wealth of detail must be attributed largely to the Prophet."
Whether Oliver relied on the notebook he had when he first met Joseph in 1829 in Harmony, or whether Joseph related the details in 1834-5 when he helped Oliver write the eight letters, it does seem apparent that, as Brother Anderson said, "the details must be attributed largely to" Joseph Smith.
One long-overlooked detail from Letter IV is that when Moroni first told Joseph about the Nephite record, he said it was "written and deposited" not far from Joseph's home near Palmyra. For Mormon and Moroni to have written the abridgment not far from Joseph's home, they would have had to have lived not far from Joseph's home.
Which, of course, is what all the prophets have taught; i.e., that the Hill Cumorah of Mormon 6:6 is the very hill in New York from which Joseph obtained the record.