Just a handy hint re number plates.
The majority of DOT approved number plates are made up of the reflective backing with the characters printed on it, pressed onto a clear panel. The glues used can often fail in places along the edge of the plate, allowing water and other dirt which accumulates and can start to obscure the characters, which becomes an MOT advisory or fail.
I found some weather proof transparent tape (ALDI special from a few month ago) which I have carefully applied folded along the top edge of my new number plates to prevent water and dirt ingress.