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.
Nearly all the Tanzania plates in this photo have been sold by German Ebay dealer mursi99 and have all been made specially for sale to collectors as a way to make money. Some of the registrations are wrong and do not exist. He has many more than these few here. He says that he bought them all in Dar-es-Salaam - no doubt in a plate shop there and nearly all the plates have never been on a vehicle. At best they are made-to-order specials.
If you search on Google Images for ‘Tanzania number plate’, you will find companies in China advertising plates identical to these, even including the same maker’s name and security etching, and there is an address in Bellvue, Colorado, USA from where small numbers can be bought.
Similar mint samples are also known from Ghana, Lesotho, Liberia, DR Congo and Cameroon.