I need your help again to make sure I got something right. It is my
interpretation that the outer table borders (actually only the outer
halves) are not included in any height or width calculations. For the
widths I'm quite sure. The CSS2 spec  says that pretty clearly:
"Note only half of the two exterior borders are counted in the table
width; the other half of these two borders lies in the margin area."
But as things go, they only speak about the start and end borders, not
about before and after but I'd say it's the same there. In collapsing
border model the table has no padding (they don't restrict themselves to
start/end there). This could be another indicator that the exterior
border halves in all directions are ignored in width and height
If that's true we have a little mistake in our "RowBorder examples"
where we calculate with 5 units of outer border for the headers and
footers instead of 2.5 units.
In real-life it also means that FO users need to specify a
space-before|after of at least half the resolved outer table border to
avoid any overlaps.