I am beginning to doubt that these are VSL uness Pamela can come up with something.
Looking closer at the Darvani site there is a section on recognition
http://users.cybernet.be/darvani/Val_Saint_Lambert_Luxval.htmwith examples which says :
Les Luxval sont "généralement " signés en relief dans le fond. Il peut être écrit "Val St Lambert Belgique" comme sur la photo n°7 ou parfois uniquement le mot "BELGIQUE" (photo n°8). Pour les productions plus récentes, simplement "VSL" (photo n°9) et également "Val Saint-Lambert Belgium" .
Tanslation
Luxval are generally signed on the base in relief. It may be say "Val St Lambert Belgique" as in pic #7 or just "BELGIQUE" as in pic #8. For more recent production simply "VSL" or equally "Val Saint-Lambert Belgium".
The "generally" does leave space for some unmarked I guess but it would seem that none of the pieces shown here are marked otherwise this would have been noted. I have re-checked mine and nothing.
So the only marked ones we know about so far are those mentioned by Kay / glasswipe.