This is what I heard many years ago - don't know if it's true or not.
Cathe filmed the ab section with her crew, but realized later that she forgot to do obliques and had to film that section again to include the missing segment.
I was on a Cathe roadtrip many years ago but back when Bodymax was fairly new and I think I remember Cathe saying something like they finished filming and went out to celebrate over pizza or something and then realized they forgot to shoot the abs so Cathe went back and did the abs portion. I'm sure I've got *some* of the story straight but it's been awhile.