There is no such thing as a genuine mint, unused, African plate. There are some collectors who specialize in African plates and they can testify that genuine, used African plates are always in fairly poor condition.
These Zambia plates were originally sold by German Ebayer robert_roman who sells a lot of samples straight from the factories in Germany. These plates have undoubtedly never been near Zambia.
Similar mint samples are also known from Ghana, Lesotho, Liberia, DR Congo and Cameroon.