This is an area of study that has recently come to light. I would like to present a quote from an article by Mel Hankal, published in a recent KRA builtin titled, Riflemen of the Cumberland. It can be read in entirety here,
http://www.americanhistoricservices.com/uploads/1/0/3/4/10348480/kra_bulletin_spring_2014_v13_1to11_lres.pdf "The gunsmith Jacob Young, second child of William Young and Elizabeth Huff, was born May 8, 1774,
on the southwest frontier of Virginia. Jacob’s father, William, was also a gunsmith and in 1776 was living
in Rowan County, North Carolina. William was an armorer under the command of General Griffith
Rutherford. In 1779 he moved his family to the Cumberland, settling on Indian Creek near modern-day
Boma, Tennessee. It was then Sumner County, North Carolina."
So you can see from this bit of verified information that the trend I spoke of was under way during the Rev. War. I know of no known rifles attributed to William Young, but there are several known, signed rifles buy Jacob Young made as early as 1790. Of the three rifles I have photographed made by Jacob Young two would be considered "high art" rifles. Another rife maker and mess mate of William Young , Thomas Simpson had also move into the Cumberland Valley of Tennessee at that time and was making rifles of the highest quality.
All of the rifles made by the men mentioned above were highly influenced buy the Virginia and N. Carolina schools as were the Kentucky gun makers on the frontier. That said the Cumberland Valley School makers along with the KY makers were very distinct in the style they developed.