I believe I have located some information regarding William ROBERTSON and the BULLARD line.
Here's what I found;
William Thomas ROBERTSON (12/19/1829, Springfield, Robertson Co., MO -- 2/3/1893, Indian Creek, Newton C., MO) son of Berry ROBERTSON (11/8/1795, NC -- aft 9/5/1850, poss Newton Co., MO) and Nancy (betw 1790 - 1794, NC -- 1865, probably Newton Co., MO)
William married Sarah Ann CLANTON (11/23/1830, Moose Creek, Mc Minn Co., TN -- 11/18/1907, Indian Creek, Newton Co., MO). She was the d/o Nancy BULLARD & John CLANTON and the grand daughter of Henry BULLARD and his wife, Leah. The great granddaughter of John BULLARD (1765, Greene Co., TN -- 1833, Claiborne Co., TN) and Agnes Nancy KERSEY (1770, PA -- abt 1851, Claiborne Co., TN).
Agnes Nancy KERSEY d/o Henry KERSEY/CASEY & Elizabeth (poss WHEATLAND). Her brother, Joseph, married Elizabeth BLACKWOOD and her sister, Elizabeth, married William BLACKWOOD (brother of Elizabeth BLACKWOOD). These BLACKWOODs were siblings of Andrew C. BLACKWOOD who married Susannah ROBERTSON d/o William ROBERTSON & grand daughter of Col. Charles ROBERTSON, of Tennessee.
I can't connect Berry ROBERTSON at this time to my Col. Charles ROBERTSON.
William Thomas ROBERTSON had siblings; Standford P. b 1824, TN; Larkin Henry b 1831, TN; Mary Ann b 1833, TN married Henry BULLARD (no other info on Henry)
William Thomas ROBERTSON & Sarah Ann CLANTON had the following children: 1. Larkin Henry Anderson Clanton (no other info) 2. James Henry Walker (b 1854, Newton Co., MO) m Emma Jane Cockrill; at least 1 child; James Osie 3. John (b 1854, Newton Co., MO) m Sarah Francis HOGAN
Source for most of the info; The Robertson Report; Book in the possession of Glenda Cronin (Family Bible & other Records)
Info on William ROBERTSON being the husband to heir of Nancy CLANTON; Source; Callaway County, McDonald County, Missouri, Wills & Administrations, "Electronic," 10/4/1872 mentions wife of William Robertson as heir of Nancy Clanton d/o Leah Bullard in Leah's will.
Please excuse any errors, I have not verified all this data.