North Carolina really has 8 classes. 1A - 1AA, 2A - 2AA, 3A - 3AA & 4A - 4AA. Teams will at times play a mixed schedule and then playoffs in their correct division. Their class are based off of ADM average daily membership.
Once the 64 qualifying teams are determined in each classification of the playoffs, the NCHSAA sub-divides the classifications based on the ADM numbers. For example, when all 64 qualifying teams in the 4-A class are determined, the 32 schools with the largest ADM numbers will go to the 4-AA playoffs, while the smallest 32 schools will go to the 4-A playoffs.