I picked up the bike yesterday. The previous owner told me he bought a secondhand frame at wim vissers shop. Wim then had it repainted at an other place. Like you I'm starting to think there was a small painting company where you could have your bike done with these decals.

So it could be that both wim visser end daan sprey had a few frames done there. According the previous owner the paint job was a special kind of process. He mentioned the word "Moffelen" what translates in powdercoating. Maybe something new at that time.

I did a quick Google check and p slikker was a well known bike shop there. They had there own brand off bikes called the "giovanni". I gave them a call but the shop has new owners. They told me that the old owner would be more then happy to talk about the history of his shop. So that might be a lead to check out.