As I said above, I simply can't imagine Inwald or Walther using BELGE or anything similar, on their glass. No way.
So why is there a BELGE mark on items that appear identical to pieces made by Inwald and Walther? They were made in Belgium (by a Belgian maker....as Ivo notes above, probably Boom...thanks for that info Ivo and Patricia). They were copies - the patterns were plagiarised. Sometimes by agreement and contract, sometimes not. It happens all the time. Here are just a few examples.
Jacobean / Milord
Inwald (Czech) and Davidson (UK)
#2266 Chunky aka English Hob & Button
Sowerby (UK) and Indiana (USA)
Rose Garden aka Rosen aka Rosor
Brockwitz (Germany) and Eda Glasbruk (Sweden)
Sunk Daisy aka Red Sunflower aka Amerika
Cambridge (USA) and Eda Glasbruk (Sweden) and Riihimaki (Finland)
The above list is just a very small selection (off the top of my head).
Glen