First of all, about Abigail Hill's birthdate:Are we quite sure that she was actually born in seventh month (Sept.) 1670, and not simply BAPTIZED at that time? I have a notation that Joanne, Elizabeth, and John Hill, her siblings, were baptized on the same date in Salem - 27April1662. Obviously they were not triplets, and apparently were not all infants at the time of their christening. While infant baptism was generally practiced, this is Salem we're talking about.Although the Zebulon Hill family doesn't seem to have been overtly Quaker, there was a Quaker community in Salem which intermarried with Quakers in other communities. If they were Quaker sympathizers who baptized their children under pressure, then for Abigail to have married the Quaker Ebenezer Allen and gone to Dartmouth is not too much of a stretch.
What I'm saying here is if these are baptismal dates instead of birthdates, then it's possible that Abigail Hill was actually born earlier than 1670.
Secondly, the name of Zebulon does not appear in the Allen family until after Abigail Hill turns up in it. Ebenezer Allen had a son Zebulon b.26May1687 who apparently died young, and also a grandson Zebulon Allen b. 1713. These would appear to be named for Abigail's father.Even if Abigail was born in 1670, she could still be the mother of Zebulon, Ebenezer Jr.,Sarah, James (who had the son named Zebulon), and Hannah.It's possible that she miscarried during the intervening years, and was still young enough to havebeen the mother of Seth and Abigail if she were born after 1660.However, some people think hers was the death recorded in Dartmouth 27March1699, making Seth and Abigail the children of some other Abigail.