Raimey: Per V-C's 1922 catalog, they still retained exclusive ownership of both the Helicobloc and Vercar marks. Not sure when the patent on the Helice system ran out, but V-C successfully sued a couple other makers in 1914 for using it.

That Belgian gun, by the proofmarks, is 1924 or later. So possible the patent had expired by then. However, although I don't know for sure, I've never seen the "Vercar" mark on any guns other than those built by V-C. I wonder if they built the gun for a Belgian dealer who had it proofed in Liege.