I must offer my thanks to OCB and others here for alerting me to the different LEZ's in Belgium. It made me check LEZ's and "Special Sticker" cities in Europe and I see I'm nowhere near up-to-date with them. The map of Europe is covered with them!
However, I've just found this interesting and potentially helpful site:- https://www.green-zones.eu/en.html
It is a commercial site originating in Germany which charges a fee to register your vehicle and/or issue a sticker for whatever LEZ or "Special Sticker" city you might plan to drive through in pretty much any European country. They have an App which looks really useful too.
Of couse,I've not used them in ernest yet but I certainly will visit their site before I plan my next European driving trip. I saw a price of €19 for registration and assume that goes up for multiple areas/countries but it seems a reasonable fee to pay them to get it right.
Imagination is more important than knowledge. Knowledge is limited - Imagination encircles the world. - Albert Einstein