This Complementary Paper presents the results of the research carried out to assess the potential legal forms of the future European Collaborative Cloud for Cultural Heritage (ECCCH). The investigation examines the governance and legal options, with particular attention to the extent to which different legal forms can support sustainability, transnational coordination, institutional legitimacy, and operational flexibility. In relation to the research design, the team investigates how existing European research and digital infrastructures have addressed challenges related to governance, funding, administrative capacity, and cross-border interoperability through different legal configurations – focusing in particular on AISBLs and comparable Association/Foundation models, ERICs, and EDICs. The study adopts a qualitative comparative research design based on 15 semi-structured expert interviews conducted between December 2025 and February 2026 with representatives of major European infrastructures and organisations. The interviews were analysed through framework analysis combining deductive and inductive coding procedures, enabling systematic cross-case comparison while preserving contextual diversity and emergent themes. The findings show that AISBL and association-based models provide high organisational flexibility and accessibility but remain vulnerable to administrative fragmentation and financial instability. ERICs offer the strongest framework for long-term institutional legitimacy and Member State commitment, although they require complex and negotiation-intensive establishment processes. EDICs emerge as governance-flexible and politically strategic instruments for European digital infrastructures, balancing adaptability with stronger governmental coordination, while raising unresolved questions concerning regulatory implementation and sustainability. By identifying the respective advantages and limitations of each model, the findings provide an empirical basis for informing the strategic choice of the future legal entity of the Cloud.