Maviskw, You're right! I agree with you, but think the point is that whether you do the vertical or horizontal borders first, you have to add the width of the border to the remaining two borders when measuring.
So, if the vertical borders go on first, then the horizontal width of the quilt must be measured after the vertical borders are on.
If the horizontal borders are put on the quilt first, then the vertical width of the quilt must be measured after the horizontal borders are on.