In a quick Google search, I pull up a 1999 article in the Cincinnati Enquirer quoting a descendant of Madison Hemings named Priscilla Lanier saying she only learned of a link to Jefferson in the 1980s, when a cousin began doing genealogical research. So at least in this case, the history of a link to Jefferson was not passed down through the generations. There wasn't an oral tradition of a link to Jefferson.
Under the year 1862, it says: "Bacon was not employed at Monticello until five years after Harriet Hemings's birth." This is not accurate.
Edmund Bacon said to Rev. Pierson that he began work at Monticello on December 27, 1800. Harriet Hemings was born in April of 1801. At the time Bacon arrived at Monticello, therefore, Sally Hemings was four or five months pregnant with Harriet. Maybe there is still a problem with chronology. But maybe not. A man is usually still the lover after impregnating the woman. Often he draws closer to her.......
Here is the specific reference: In "Jefferson at Monticello" by Rev. Hamilton W. Pierson (published 1862), Edmund Bacon said the following:
"I went to live with him [Jefferson] the 27th of the December before he was inaugurated as President."
Jefferson was inaugurated in 1801. Therefore, Bacon began work at Monticello on Dec. 27, 1800.
Bacon was promoted to overseer of Monticello in 1806. But he began work there in 1800. It seems that his eye-witness account was dismissed due to poor attention to detail on the part of Monticello researchers and this committee.