Probate and chancery court records of Louisa County, Virginia prove without a doubt that Susannah CRENSHAW who married John BURNLEY in 1785 in Louisa County was the daughter of William CRENSHAW and Susannah CARR of that county. Susannah Crenshaw Burnley isn't my direct ancestor, but she was the sister of my ancestor Charles CRENSHAW, and I've found data on her while working on the whole family.
Many family trees make the mistake of listing "Susannah Crenshaw" (wife of John BURNLEY) as the daughter of Nicholas CRENSHAW and Mary CARR. Nicholas and Mary did have a daughter "Susanna" (per their bible record, born 20th October 1767), but that Susanna did not marry John BURNLEY.
Many family trees, including a dozen or more submitted databases to LDS FamilySearch, also cite an exact BIRTH DATE for Susannah, daughter of William CRENSHAW & Susannah CARR, as "20 Oct 1767." This date, however, is actually the birth date of Susannah, daughter of NICHOLAS CRENSHAW and Mary CARR. See Nicholas' bible record transcript originally published in National Genealogical Society Quarterly, Vol. 32, No. 4 (later included in "Virginia Bible Records" by Jeannette Holland Austin).
William CRENSHAW and Susannah CARR's daughter Susannah was probably born about 1760-1764, estimating back from the calculation that she married at age 21 or older in 1785. She could have been born earlier but not later than about 1764, since she was apparently of legal age to marry (21) and didn't need to have her father's consent when the marriage bond was given in 1785.
The Burnley-Crenshaw marriage bond is cited in the Edward Pleasant Valentine Papers:
Marriage Bond of John Burnley and Susannah Crenshaw. Bond dated 13 Decr. 1785. James Duke, security.
Her sisters' marriage bonds are cited in the Valentine Papers as well, some WITH their father's written consent, such as Ann's (Nancy's), even though they were already of legal age:
"This is to certify that my daughter Ann Crenshaw is of age & as she desires license for Marriage I should be glad you would grant them. Wm. Crenshaw. Test: Chas. Crenshaw."
We could take this difference in how the Crenshaw girls' marriage bonds were written to mean that Susannah was clearly age 21 or older and her being of legal age wasn't questioned, as it might have been with several of her sisters. But also William Crenshaw could have given written consent for Susannah's 1785 marriage, and this consent document just didn't survive for us to read today.
If Susannah Crenshaw and John Burnley are your ancestors, I hope that you'll list them accurately in your family tree and that you'll make corrections if you have Susannah with the wrong parents and birth date.
There are lots of confusing details about early Crenshaws, and we should all want to have the most factual family trees possible. I'm always glad to share research notes with anyone interested, and glad to make corrections to my own data if more sources and proofs turn up!