Good point, but the Thornicroft's giraffes in Zambia look like they are very closely related to the Masai giraffes, if not directly a geographically isolated population of Masai giraffes. This is based on mitochondrial DNA sequences found in Russell Seymour's PhD thesis.
@DAVID Brown: Good point too. As in so many cases when classifying species/subspecies, it is a question of which scientist you will follow/believe (No matter how your decision is, a few years later it will be wrong either, because another scientist will have found "evidences" for another kind of relation)...