This will be a short entry and only partially about grading pants. Mostly it is about Handford's notation and what caused me confusion.

Now notice the little black triangle under the point of origin. Handford uses this triangle in many drawings. I interpreted those triangles to mean the "point of origin" and that is where I messed up.
Compare the drawings for pants of women (pg 77), men (188-189), and children (219). You'll notice that Handford adds or drops those black triangles almost randomly. Some drawings have them, some don't.
The black triangles don't indicate "point of origin". Instead, I think Handford is borrowing the notation from geometry where it means "right angle". Your direction arrows should be perpendicular - at 90 degrees. If you look at the pants drafts (sorry no more drawings for today), you can see his direction arrows are drawn down the center of the pant legs with two black triangles - meaning the lines should all be perpendicular. In my head, I was seeing "point of origin" or (0,0) on an X-Y coordinate plane. Interpreting things this way caused me to move my pattern pieces incorrectly (my own dumb fault for trying to over analyze things).
Anyway, by nesting my pieces I found my error and realized Handford's direction arrows do not always show the point of origin on all of his drawings. They just show direction.
Clear as mud?