Just a guess... I don't have the Sias books with me so I won't be able to check intormation until this summer (if I'm reminded to do so at the time).
Nabby might be Nathaniel. My ggggggrandparents Charles & Jane Sias moved to Derby Vt. in 1802. They had a son Nathaniel, born abt. 1780, so he'd be about the right age. Derby is about 20 miles from Troy.