Based upon census records, there two possibilities for the Tandy Marshall to whom Gabriel Finn was said by Caleb Wilson to be indebted circa 1840. Those were Tandy Marshall (born 1812, son of Thomas Riley Marshall, in Stokes County) and Tandy Marshall (born 1808 in Stokes County). There were two other persons by that name, one 12 years old in 1840 and the other whose full name was Matthew Tandy Marshall and who went by Matthew.
This Tandy Marshall (son of Thomas Riley Marshall) was later involved in a land transaction with Joseph William Marshall, a grand-nephew of Gabriel Finn, and also named one of his sons Joseph William Marshall. Circumstances suggest this Tandy Marshall as the more likely to have known Gabriel Finn.
Regarding the naming of Tandy's son, it should be noted that Tandy was born in 1812 and that his son Joseph William Marshall was born in 1854, two years after Joseph Marshall's boy Joseph William was born in Danville VA. So Tandy should be view more as a contemporary of the elder Joseph Marshall than of Joseph William (born 1852). Also, it is quite possible that the naming of Tandy's son is a clue to the "W" in Joseph W. Marshall's (1802-1870) name. Although it would make perfect sense for his name, too, to be Joseph William Marshall (named for his grandfather, William Marshall, of Brunswick County VA. But there was the other example of his brother Edward Wilson Marshall.
Sons of Zachariah Marshall of Person County NC
With the exception of William Swaine Marshall, finding documentation linking other possible children to Zachariah Marshall and his wife, Sarah (Salley) Finn, has been difficult. The effort began by using census records to find the most likely parents for Joseph Marshall (b 1802). Zachariah (aka Sack, Sacky, Zach and even Isaac) of Person County, North Carolina, appeared the best candidate. When the brother relationship between Joseph and Edward Wilson Marshall became apparent, this too was consistent with them having Zachariah and Sarah as parents. There was, however, no documentation other than ticks on pre-1850 census records to support this.
Fortunately, a large number of Person County records are online at familysearch.org. These include the annual lists of taxables. [Person County was formed in 1792 from the eastern half of Caswell County. Caswell County had been formed from the northern half of Orange County in 1777. St Luke's District appears to have been approximately the southwest quarter of Person County] Here are the entries for Marshalls:
No Marshall entries prior to 1797 (go back to 1792 when Person County was formed from Caswell Co)
1796 Gabriel Finn (St Luke's District; no land)
1797 Jesse Marshall (200 ac); Sack Marshall (no land) (St Luke's District)
1798 Sack Marshall (no land); Gabriel Finn (no land); Elizabeth Finn (73 ac)
1799 Sack Marshall (577 ac); Gabriel Finn (no land); Elizabeth Finn (70 ac)
1800 no entries for Marshall; Elizabeth Finn (70 ac)
1801 Zachariah Marshall (no land); Gabriel Finn (no land)
1802 no entries for Marshall; Gabriel Finn (no land)
1803 no entries for Marshall; Gabriel Finn (no land)
1804 no entries for Marshall; Gabriel Finn (no land)
1805 no entries for Marshall; Gabriel Finn (no land); Edward Finn (no land)
1806 no entries for Marshall; Gabriel Finn (no land)
1807 M William Marshall (no land); Gabriel Finn (no land)
1808 no entries for Marshall or Finn
1809 no entries for Marshall; Gabriel Finn (no land)
1810 M William Marshall (no land); no Finn
1811 M William Marshall (no land); no Finn
1812 William Marshall (no land); no Finn
1813 Sackey Marshall (230 ac); no Finn
1814 Sack Marshall (230 ac); no Finn
1815 Sacky Marshall (230 ac); William S Marshall (no land)
1817 Sacky Marshall (162.5 ac); M William Marshall (no land)
1818 Sacky Marshall (162.5 ac)
1821 Sacky Marshall (162.5 ac) "do Robt Purkill (sp?) (65.5 ac)
1822 Sack Marshall (151.5 ac)
1823 M William Marshall (no land); Sackey Marshall (151.5 ac); William S Marshall (11 ac)
1824 Sackey Marshall (151.5 ac); William S Marshall (11 ac) do Joseph Marshall
1824 inventory of Thomas Phelps estate notes judgment v Sacky and N Norfleet for $99.50)
1825 William S Marshall (11 ac) do Sackey Marshall (151.5 ac)
1833 William S Marshall (112 ac); Charles Marshall (no land)
1834 William Marshall (112 ac)
1835 William S Marshall (112 ac); John Marshall (no land)
1836 William S Marshall (112 ac); John Marshall (no land)
1837 John Marshall (57 ac); Edward Marshall (no land); William S Marshall (112 ac)
1838 Edward Marshall (no land); William S Marshall (112 ac)
1838/9 Sacky dies
1839 Gabriel Marshall (no land); William S Marshall (112 ac); John Marshall (no land)
1840 William S Marshall (112.5 ac); Edward Marshall (no land); John Marshall (60 ac)
1841 William S Marshall (112.5 ac); Edward Marshall (no land); John Marshall (57 ac)
1844 William S Marshall (112.5 ac); John Marshall (172.5 ac)
It appears that entries are made by name only for persons (generally males) over the age of 21. Joseph Marshall appears only once (1824, when he would have been 21/22 years old). Edward appears first in 1837 when he, too, would have turned 21. Gabriel, previously unknown to me, appears in conjunction with William Swaine Marshall in 1839, suggesting that he had been born in 1818. Since no other Marshall families were discovered, and these entries occurred within a few lines of each other, this appears to be strong evidence that Zachariah and Sarah were the parents of William Swaine, Joseph, Edward, John and Gabriel Marshall. The identity of M William Marshall is unknown. Also, Person County would have been the birthplace of Gabriel, because Zachariah is shown to have been there in 1818. He appears to have been named for his uncle, Gabriel Finn (who is found in St Luke's District, Person County beginning in 1796). This also agrees with the counts of persons in Zachariah's (Sack's) household in the census records. These are also the only records so far known demonstrating that Sack Marshall's real name was Zachariah.