This presentation introduces the Open Music Observatory and its national pilot, the Slovak Comprehensive Music Database, as emerging pillars of a federated European music data ecosystem. It outlines the metadata gaps identified in the Feasibility Study for a European Music Observatory and demonstrates how open data reuse, cross-stakeholder collaboration, and interoperable knowledge graphs can address missing, fragmented, or inaccessible music metadata. Using Slovakia as a case study, the presentation shows how poor metadata quality affects local repertoire visibility—such as the misclassification of small repertoires in recommendation systems—and how open, semantically aligned dataspace infrastructures can improve discoverability, rights management, and cultural statistics. The presentation highlights practical applications including entity reconciliation, multilingual authority control, and connections between library, rights-management, and streaming metadata. By implementing the European Interoperability Framework across technical, semantic, organisational, and legal layers, the Open Music Observatory demonstrates a scalable, ethical method for building cross-domain cultural data services capable of supporting policy, research, and public access.