Critical resources explained

We are having problems understanding critical resource list, that we show in attached picture (resource names have been deleted).

The table is clear if we exclude "overbook mode" and "including overused" columns.

Doubts:
"overbook mode" and "including overused" seems to be misleading or inverted: from manuals it looks like overbooked is the sum of normal and overbooked, and including overused seems to be the difference, but we ask why not to use more precise words, and why use different words (overbooked and overused).
Any way you want to call them, the three planned columns dont' match.

Margin column seems to be the difference from normal mode and available time, while we feel it should be the difference among (normal + overused) and available (unless making a double raport, one related to normal mode and one related to total work).

As final conclusion, we are in confusion.

What are we missing?