If Mack was the son of George, then the story of dropping the "r" from his name does not line up with the first two U.S. Census records in 1790 and 1800 (George is not in the 1790 Census). In the 1800 Census, George is living in South Carolina (Spartenburg District) as head of household. The spelling is Calton, not Carlton, which means that Mack did not drop the "r" per the legend after stealing a horse and fleeing to the Appalachians. Another Calton listed in Spartanburg as a head of household is Elisha. There is a John Calton is Abbeville, SC, and a Lindsey Calton in Salisbury, NC.
Though the fluctuation between Carlton and Calton happened then as it does now, those early census' are consistent enough to show that the actual spelling in early U.S. history was Calton. Also note the Gaelic spelling for Calton is McCalden. The spelling may have changed prior to immigration to the U.S. Many McCaldens, as well as Calton's, immigrated later than George's father in the 1800s.
