I think I am finally on to something:
The Thomas Stafford who lived in Springfield, Vermont had two known children, Clarissa and Stephen. These births were recorded in 1795, leaving the potential for later children. In fact, the 1800 census shows a household of 1 male < 10 years old , 1 male 16-26, 1 male 45+ , 3 females < 10, 1 female 10-16, and 1 female 26-45.
Clarissa married one Lawson Bruce and lived in neighboring Chester, Vermont. In 1870, there was a 77 year old Ambrose (no surname shown, presumed Bruce by the transcriber) living in the same household as Clarissa. I cannot find another record for a matching Ambrose Bruce. Sebrina's 77 year old husband Ambrose Hastings was missing from the 1870 census. This seems like too much of a coincidence for them not to be the same person.
Taking a step further, were Clarissa and Sebrina sisters, making Thomas Sebrina's father?
