What contention are you talking about? The fact that Grant owned a slave from sometime in 1858 until March 29, 1859 is supported by letters found in "The Papers of Ulysses S. Grant, Vol. 1 through 4". In a letter that Grant wrote to his father dated March 21, 1858 he said, "I have now three Negro men, two hired by the year and one of Mr. Dent's." Whether the third man is William Jones in unclear but it's highly likely that it was. In any case, Grant wrote a later letter to his father dated October 1, 1858 and said, "Mr. Dent thinks I had better take the boy he has given Julia along with me, and let him learn the farrier's business. He is a very smart, active boy, capable of making anything, but this matter I will leave entirely to you. I can leave him here and get about three dollars per month for him now, and more as he gets older." That seems to indicate that Jones was actually given to Julia Grant, but legally property of the wife became property of the husband so Grant can be said to be the owner of Jones. In any case the fact that Grant freed the man on March 29, 1859 is supported by the manumission papers filed with the state of Missouri.
By March 1859, when Dent gifted Jones to Grant, Grant freed Jones.What contention are you talking about? The fact that Grant owned a slave from sometime in 1858 until March 29, 1859 is supported by letters found in "The Papers of Ulysses S. Grant, Vol. 1 through 4". In a letter that Grant wrote to his father dated March 21, 1858 he said, "I have now three Negro men, two hired by the year and one of Mr. Dent's."What is your source for the assertion that Jones was given to Grant in March 1859 rather than sometime in 1858? (I have seen nothing to prove either contention.)
My post (to Capitan Refugio) referred to the following contention of Capitan Refugio at #1825:
It has sometimes been suggested that US Grant himself owned slaves. This is a misrepresentation. For a brief period in 1858-1859, Grant employed three African men. In a letter, Grant wrote, "I now have three Negro men, two hired by the year and one of Mr. Dent's." The Dent slave was a 35-year old mulatto named William Jones. By March 1859, when Dent gifted Jones to Grant, Grant freed Jones.