Without being in the factory and knowing their machinery, do you suppose that it's their way to "sew" the pleats into position for assembly? In other words... we're supposed to take a stitch in the pleats to hold them while we sew the hips down. This may be where they stitch for the taper and final sewing.

It makes sense, but doesn't explain what they would be doing to damage the fabric. Perhaps the wool methods don't work too well on canvas, duck, or whatever?

Terminology omitted for everyone. I hope it makes sense this way!