Civil registration of births and deaths is a foundational State function, but its increasing digitisation and centralisation raise a distinct constitutional question: how far may the State aggregate, link, share and reuse population-scale civil-registration data beyond the immediate purposes for which it is collected? Birth and death records support legal identity, public administration, demographic planning and the delivery of public services, yet their integration across government databases can also intensify risks to informational privacy, purpose limitation and institutional accountability. This paper examines these concerns through doctrinal, analytical and comparative legal research. It analyses the Registration of Births and Deaths Act, 1969, as amended in 2023, the constitutional right to privacy recognised in Justice K.S. Puttaswamy (Retd.) v. Union of India and developed in the Aadhaar litigation, and the Digital Personal Data Protection Act, 2023 together with the Digital Personal Data Protection Rules, 2025 and their phased implementation. The paper focuses not on the legitimacy of statutory civil registration itself, but on the downstream storage, aggregation, interoperability, sharing and secondary use of the resulting data. It finds that administrative necessity at the point of registration does not, by itself, justify unrestricted subsequent dissemination or reuse. Comparative analysis of Estonia, the European Union and the United Kingdom further demonstrates that effective digital government need not depend upon indiscriminate data concentration. The paper therefore proposes a model of accountable interoperability in which data exchange is governed by clearly defined statutory purposes, data minimisation, role-based access, auditable transaction logs, retention discipline, correction mechanisms, layered security and independent oversight. Such an architecture can strengthen Digital State Capacity while preserving constitutional limits on governmental informational power.