I’d say this is great, as well as an opportunity! If they use Openstreetmap, then surely they don’t mind if we use their data. This could be a win-win situation: what if we could use the data and map they already made from our taxpayer money for OSM mapping, for instance by making the cadastre map available as a background for OSM editors? Anybody who knows how to make a background available in iD and JOSM? Do we need their permission, or could we just do it? Anybody who knows how to approach them and propose this? Anybody who knows what the copyright status of their data and their map is? There’s probably no better source in Bulgaria for data on building shapes and nature, street names, locality names, etc.