(edit conflict) For what it's worth, one of the refs I added is a Google Book link: Chapter VI: Quadripoint Theory. It is mainly focused on the case of the Caprivi Strip area and the borders of Namibia, Botswana, Angola, and Zambia. This classic case was ruled, I think, a "near miss"although it may still be unresolved. I think it was once mentioned on this page but no longer seems to be.