Metadata management is an essential condition to follow the FAIR principles. Therefore, metadata management was one asset of an accompanying project within a funding scheme for registries in health services research. The metadata of the funded projects were acquired, combined in a database compatible with the metamodel of ISO/IEC 11179 “Information technology – Metadata registries” third edition (ISO/IEC 11179-3), and analyzed in order to support the development and the operation of the registries. In the second phase of the funding scheme, six registries delivered a complete update of their metadata. The mean number of data elements increased from 245.7 to 473.5 and the mean number of values from 569.5 to 1,306.0. The conceptual core of the database had to be extended by one third to cover the new elements. The reason for this increase remained unclear. Constraints from the grant might be causal, a deviation from an evidence-based development process as well. It is questionable, whether the revealed quality of the metadata is sufficient to fulfill the FAIR principles. The extension of the metamodel of ISO/IEC 11179-3 is in agreement with the literature. However, further research is needed to find workable solutions for metadata management.