The early records that Howard Durie left were extensively documented through legal records and first person narratives. However, the records of the later generations relied on questionnaires sent to family members and some of those reports were not as accurate. The information on Jeff Seth may have been supplied by one of his half siblings or even by a cousin. The name Rovana may have been a first or middle name of Iris's or the supplying relative may have given the wrong name. Most of the information on this family between 1690 and the early 1800s is very reliable. Info from about 1880 on . . . not so much.
I missed a few details in my last post. Francis Marion's 4th wife, Anna, who outlived him remarried 3 Dec 1904 to James W. Pretty. Francis Marion is buried in the Shaul Cemetery in Ottumwa.
Later in the book there is a contradiction to the information I gave you from page 200. According to page 255, Samuel Omer and Mabel (Myrtle died young) were the children of Francis Marion and Mary E. Cook and not the children of Anna Forbes. Only Blanche and Jeff Seth seem to be the children of Anna.
Samuel Omer (a half-sibling of Jeff Seth) and his wife Maude M. Hasty used the DuRee form of the name. He is also the last person recorded as having possession of a family bible belonging to Samuel Durie b. 1775. Maude was county recorded for Keokuk County, IA for many years and furnished Howard Durie with photocopies from this bible. They adopted a niece of Maude's, Lucille born about 1904. I assume that she inherited the bible. She married a D. Louis Stark, but the information ends there.
There is no further information in the book on Blanche. Is that your grandmother? I'd love to have her information if that is possible.