The brook trout stocked by North Carolina are all Northern Strain. Of North Carolina's wild brook trout, approximately a third or so are all southern strain, about 10-15 percent or so are all Northern Strain, and the rest are mixed strain with varying degrees of Southern strain and Northern Strain (i.e. the brook trout in one stream may have 80% Southern Strain genetics and 20% Northern Strain genetics or vice versa or any combination thereof). Interestingly, most of the Southern Strain streams in NC are Gulf of Mexico drainages. There are only a few streams in NC that flow into the Atlantic that are pure Southern Strain.
It is my understanding that Tennessee has a much higher percentage of streams that are pure Southern Strain, though NC probably has much more brook trout water.