Based on a rather diffuse research with a rather limited sample group. Often quoted, but lacking credible merit. I personally believe it should be discounted and no longer cited as a valid source.
I think in reality there are at least three subspecies in Africa: one in South and East Africa, one in North Africa, and one probably Extinct in Zanzibar. You see this subspecies pattern in other large cats such as Lions and Cheetahs so it's likely Leopards follow similarly, and there's no doubt in my mind that the Zanzibar cats are/were distinct.
~Thylo