There are no folds on the apron in the picture. There really is a variation in the width of the green stripes on the apron. The back is actually pleated to the same stripe; what happens is the green disappears from the pattern, then comes back. Then a new piece of slightly different material is attached to form the last few pleats (one of them much deeper than all the rest)and the under panel (terminology?). The second piece of fabric has no green stripes at all. I'll post some more pics when I can.

My first guess is that it as the result of some wartime shortage of fabric, or a rushed weaving making for either a mistake, or a substitution of one yarn for another to keep production going. I wish I knew more.

After wearing it last night for a long Burns evening, I can tell it will fit better if I move the straps back to their original places.
John