I think it is very safe to say that the William Jackson who executed his last will in 1774 in Martin C. is not a son of Daniel Jackson of Pasquotank Co., because we see Daniel's son living in Pasquotank in 1754 and 1764, transacting on land involving his brother Daniel Jackson, Jr.... e.g.,
8 Nov 1754: William Jackson of Pasquotank to Daniel Jackson. Wits. Moses Jackson, David [D] Jackson.<ref>William Jackson to Daniel Jackson, 8 November 1754. "Deed records, 1700-1910; general index, 1700-1915. Deed records, v. F-G 1755-1761." ''FamilySearch,'' film # 7,517,573, [https://www.familysearch.org/ark:/61903/3:1:3QS7-9983-6GQX page F&G:11 / image 14].</ref>
20 Nov 1764 William Jackson of Pasquotank Co. to Patrick Pool of same, 112A bounded by land sd. Pool has lately taken up and a piece of land sd. Pool purchased of Daniel Jackson.<ref>William Jackson to Patrick Pool, 20 November 1764. North Carolina. County Court of Pleas and Quarter Sessions (Pasquotank County). "Deed records, 1700-1910; general index, 1700-1915. Deed records, v. D-E 1761-1770." ''FamilySearch,'' film # 7,517,574, [https://www.familysearch.org/ark:/61903/3:1:3QS7-L983-6VQ8 page D&E:300 / image 306].</ref>
... and meanwhile, William Jackson of the Tyrrel Co./Edgecombe Co. border region (later becoming Martin County) appears there:
13 November 1754: John (x) Williams ''late of Tyrrel Co.'' to William Jackson of Tyrrel Co., for divers causes and £20 current money of Virginia, 225A ''partly in Tyrrel Co. and partly in Edgecombe Co.,'' bounded beg. a pine Daniel McLains or McLams corner tree mentioned in a deed from Earl Granville date 31 Oct 1752, running E 220 poles then W 220 poles then S 220 poles to the first station [these bounds are missing a northward line, see the following], being half of land granted in aforesaid deed from Granville to said WIlliams, being half of land granted 31 Oct 1752 to said Williams, with houses, orchards, etc. Wits. Humphry Bate, Sarah Bate, Ann Grish.<ref>John Williams to William Jackson, 13 November 1754. North Carolina. County Court of Pleas and Quarter Sessions (Tyrrell County). Deeds, 1736-1920; general index to deeds, 1729-1961. Deeds, v. 1-3 1736-1759." ''FamilySearch,'' film # 7,519,076, [https://www.familysearch.org/ark:/61903/3:1:3QSQ-G98Q-3XNT page 3:62 / image 507].</ref>
25 June 1774: William Jackson of Martin Co. to Bila Williams Jackson, for divers causes and L50 current money of North Carolina, 225A in Martin Co., b. beg. a pine Daniel McLams or McLains corner tree mentioned in deed from Earl Granville date 31 Oct 1752, running E 220 poles, N 200 poles, W 220 poles and S 200 poles, with houses, orchards, etc., being one [half] of grant from Granville to John Williams. Wits. Sam'l Turner Everitt, John Lewelling, Nathan Mayo.<ref>William Jackson to Bila Williams Jackson, 25 June 1774. Martin County (North Carolina). Register of Deeds. "Deeds, 1774-1941; index to real estate conveyances, 1772-1963. Deeds, vol. A Jan 1774-Sep 1787." ''FamilySearch,'' film # 7,548,557, [https://www.familysearch.org/ark:/61903/3:1:3QS7-L9DX-W45D page A:33 / image 32].</ref>
I also now believe it is unlikely that this William Jackson was a son of Thomas Jackson of Bertie Co. If Thomas Jackson named his children in age-order in his last will, then his son William was born around 1740 -- too young to be buying land in Tyrrel in 1754.
I have to finish abstracting deeds in Edgecombe Co., and I need to track down deeds in Halifax Co. (the indexes there are a mess), but I am starting to suspect Thomas' son was living in Halifax Co. after the decease of the Martin Co. man. This is all complicated by the creation of Halifax Co. and later Martin Co. where the border of Edgecombe and Tyrrel had been in the earlier part of the 1750s.