How does one figure out something which one can't find in Scott is a revenue?
1) Go to Google and type in "Belgium revenue stamps" and a page will come up, then click on the IMAGES tab at the top of the page. All kinds of pictures of Belgium revenues will come up.
2) Go to eBay
and click on the "Stamps" category. Type in "Belgium revenue" and all kinds of pictures of Belgium revenues will come up.
I use both of these methods.
Hope this helps you,