The lug cut-out seems to back up the Derycke sticker. Derycke is one of the Belgian frame builders known to have supplied 'no name' frames to quite a few bike shop owners here in the Benelux region who either didn't build frames themselves but wanted something decent, or frame builders who wanted something more affordable next to their own hand-built frames. The Deryckes I've seen all had Reynolds 531 decals IIRC.

I have one myself, a Giovanni. The faux Colnago cut-out is apparently a Derycke trademark.