> nearly all Ancestry trees show Silence Dimmock to be the daughter
> of Bethia Chipman and Timothy Dimmock

Although Ancestry trees can provide useful suggestions, some contain information copied from other places which is erroneous. The authoritative sources for information on the early generations of Mayflower descendants are the publications of the General Society's Five Generations Project. Because they contain recent and thorough research by recognized Mayflower scholars (many of the FASGs) and they are fully documented those are the first sources examined by state historians and the HG when vetting lines. The MF5G books have not yet reached the descendants of Hope Howland, so I would suggest checking:

Elizabeth Pearson White, "John Howland of the Mayflower, Volume Three" (descendants of Hope) (Camden, ME: Picton Press, 2008)

to see what light it may shed.

There appear to be a number of questions about the marriages of Bethia Chipman. For a discussion see p. 72 of:

Susan E. Roser, "Mayflower Increasings (For Three Generations)" (Baltimore: Genealogical Publishing Co., 2nd Edition 1995)

Timothy Dimmock married Abigail Doane 17-Mar-1702/03, according to Roser, so if Silence was born after that date she was the cild of Abigail.

Dale H. Cook, Member, NEHGS and MA Society of Mayflower Descendants;
Plymouth Co. MA Coordinator for the USGenWeb Project
Administrator of http://plymouthcolony.net