That’s a very common pattern, seen on passenger cars from Billmeyer & Small, Jackson & Sharp, Laconia, Carter Bros, Brill and others. The narrow board below the belt rail matches the spacing between the windows, while the wide boards under the windows are half the width of the window. If you look at my coach 13 above, you’ll see a similar pattern, though the spacing between the windows is wider than on the CR&N cars.
Here’s another version, without the belt rail:
Later,
K