MacGuffey/MacGuffie/MacGuffock was accepted as a sept of Douglas by CDSNA at its organization in 1975 based on the original list from the book Scots Kith and Kin.
According to The Douglas Archives, [http://www.douglashistory.co.uk/history/Septs/MacGuffog.htm]
“Recorded in the spellings of MacGuffog, MacGuffie and MacCuffie, but more generally in the short forms McGuffog, McGuffolk, McGuffie and McCaffie, this is an early Scottish surname. It is unclear as to the origin, which may be locational from an estate called Guffokland, believed to have been near Stewarton in Argylshire, or possibly a patronymic from the early Gaelic name MacDabhog, which translates as the son of David. It is said that the family of McGuffok were once very powerful in Central Galloway, with Patrik McGuffok being a herald on behalf of Sir Robert Bruce, and making statements on his behalf in the year 1291. It was probably his son as Richard McCuffok, who in 1329 was confirmed as the owner of lands in "Kelinsture and Cloentes" for services to King Robert, The Bruce (1306 - 1329). Other recordings from that period showing an early spread of the name through the country include: John McCoffot, the rector of Gewilston in Galloway in 1347, Ellen McGuffok in Aberdeen in 1376, and Thomas M'Guffok, who is recorded as being secretary to Margaret, the countess of Douglas, in 1429.
The name spelling as McGuffie is apparently first recorded in 1513 when Colonel John McGuffie, was one of the list of Scottish officers killed at the battle of Flodden in 1513, whilst in 1570 a Provost M'Guffie was recorded in Wigtown, and John M'Kuffie in yet another variation of the spelling, was a councillor at Kircudbright.“
Black, in Surnames of Scotland (p. 507), under the surname Macguffog says “The name of an ancient and once powerful that at one time possessed lands in central and western Galloway” and goes on to state:
Gilbert M’Guffok was a tenant under the Douglas in Mikilbrekauch in the parish of Buittle, 1376… Thomas M’Guffok who was secretary to Margaret, countess of Douglas, 1429, may be Thomas Mcguffok who held the church of Glencarn in 1450.
Black, George F. The Surnames of Scotland: Their Origin, Meaning, and History. Edinburgh: Birlinn,
The Douglas Archives, http://www.douglashistory.co.uk/history/Septs/MacGuffog.htm