Steve's right... again. In fact, you can use any multitude of pieces as long as the seams are deep in the pleats. I know one kiltmaker that actually uses one piece for the front apron, one for the pelates on the left, one for the pleats on the right, and one for the under apron. The pieces are already surged and in-stock for assembly. The differenct waist sizes will determine which length of piece is used for the pleats.
I would not suggest it, but I've seen one kilt that had alternating pleat colors (green, white and gold). the work to join all that must have been a real pleasure.