58-Belgian made to order specials
In Belgium only one plate is officially provided and has the official stamp embossed into it. The second plate must be provided by the owner, has no official mark and there are many plate shops that make whatever plate you want.
This photo is of owner provided, unused (mint) Belgian plates that have been made specially for selling to collectors. They are of rare types so that a profit can be made but they have never been on a vehicle (all look mint even though some have holes) and have no official mark.
It is up to you, if you want a genuine used Belgian plate, don't buy mint ones without the official stamp. If you are happy with a made-in-Belgium special for collectors, then carry on.
These come up fairly regularly on Ebay from various sellers.