Facts and Events
There is 1,058 vital record available on MyHeritage for Mary Kincaid, including birth records, marriage records, and death records. Vital records are historical records that are typically recorded around the actual time of the event, which means they are likely accurate. Vital records include information like the event date and place, and the person's occupation and residence. Vital records also often include information about the person's relatives. For example, birth and marriage records include names of parents and divorce records list the names of children.
Mary Dugger, widow appeared on the 1774 tax list in Surry Co., NC. The area she lived in later became Wilkes Co., NC and she appeared there in 1785. By 1787 she was over in the Watauga River area of what is now Carter Co., TN.
Those three records are all we have for Mary Dugger, widow. She was indeed a widow for she was referred to as such on one of the records. None of the records say who her husband had been though.
Someone in the early 20th century made the assumption that Mary was the widow of the the supposed pioneer Julius Caesar Dugger. He obviously had to have a wife, and Mary was a widow, so therefore putting two and two together, they came up with him as her husband. A natural assumption of course. Though based on faulty information. There was no person named Julius C. Dugger, nor had their ever been. (See his page for commentary on that subject.)
The next assumption they made was based on the first. Julius C. Dugger was said to have come to Tennessee in 1766 with Andrew Greer. Somehow or another they assumed they were brothers-in-law, and therefore married to sisters. Mr. Greer's wife was a Kincaid. Therefore Mary Dugger must be also. Thus we have Mary Kincaid, wife of Julius C. Dugger.
Genealogist must work from source documentation. It is okay to make assumptions when there is circumstantial evidence to back it up, but making assumptions on top of other assumptions just compounds problems.
Robert T. Nave had this to say on this subject