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.htm
with examples which says :
Les Luxval sont "gĂ©nĂ©ralement " signĂ©s en relief dans le fond. Il peut ĂȘtre Ă©crit "Val St Lambert Belgique" comme sur la photo nÂ°7 ou parfois uniquement le mot "BELGIQUE" (photo nÂ°8). Pour les productions plus rĂ©centes, simplement "VSL" (photo nÂ°9) et Ă©galement "Val Saint-Lambert Belgium" .
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.