Here is a summarization of John COE's Census data for 1810 to 1840:

John COE: 1 - 0 - 0 - 1 - 0 -- 2 - 0 - 0 - 1 - 0 -- 1 slave [Surry, KY 1810]
John COE: 3 - 1 - 0 - 0 - 1 - 0 -- 1 - 2 - 0 - 1 - 0 -- 1 slave [Cumberland, KY 1820]
John COE: 0 - 0 - 2 - 1 - 0 - 0 - 1 - 0 - 0 - 0 - 0 - 0 - 0 -- 1 - 1 - 0 - 1 - 0 - 0 - 1 - 0 - 0 - 0 - 0 - 0 - 0 -- 3 slaves [Cumberland, KY 1830]
John COE: 0 - 0 - 0 - 1 - 0 - 0 - 0 - 1 - 0 - 0 - 0 - 0 - 0 -- 0 - 0 - 1 - 1 - 0 - 0 - 0 - 1 - 0 - 0 - 0 - 0 - 0 -- 11 slaves [Cumberland, KY 1840]

In 1810, the famale in Joe COE's household, presumably Nancy SCOTT, is shown to be age 26 to 44 (b abt 1766-84). The one male child and two female children under age ten would seem to suggest that John and Nancy married after 1800 and more likely sometime about 1803 to 1807. Nancy seems likely to be at the younger end of the indicated age range, given the age at which young women then commonly married.

Thus, the asserted date and place of the marriage cited by most COE researchers seems to be quite reasonable.

In 1820, the age of the oldest female residing in John COE's hosuehold is again shown to be age 26 to 44 (b abt 1776-94).

In 1830, the eldest female in John COE's household seems to be age 40 to 49 (b abt 1781-90).

In 1840, the eldest female in John COE's household seems to be age 50 to 59 (b abt 1781-90).

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The 1850 Census show both John COE and Nancy COE to be age 65 (b abt 1785).

All of the Census records are very consistent with the 1785 indicated year of birth except for the 1810 Census, but the deviation from the implicit range is so minor that it could easily be explained by a small error in the reported age for Nancy at either 1810 or 1850.

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I mention this simply to observe that there IS some primary evidence which would tend to support the idea that John COE was only married once.