Mapped Is Not Equivalent: Traceable mappings, qualified mappings, and the governance questions between the EHDS building blocks

The European Health Data Space relies on mappings between national and shared terminologies. A mapped code can be correct and still carry less information than the original. This working paper reviews what is already in place, namely national mapping processes, the cooperation between LOINC and SNOMED CT, and Implementing Regulations (EU) 2026/2083 on MyHealth@EU and (EU) 2026/2098 on dataset metadata. It then asks where three questions are answered together: what a mapping asserts, what it is valid for, and who stands behind it. It distinguishes traceable from qualified mappings, notes that legal requirements differ between cross-border care, secondary use and AI, and closes with four questions that implementers, data holders and buyers can use to test their own position. Corrections are welcome.