The rapid digitization of cultural heritage during the COVID-19 pandemic led to a surge in the creation of 3D models. However, the absence of standardized metadata and documentation practices has hindered their interoperability, discoverability, and reuse. This article presents the development of the 3D Core Data Model (3D-CDM), initiated within the DFG 3D-Viewer project, as a proposed solution for improving metadata harmonization. Drawing from comparative analysis across several German infrastructure projects and aligning with established standards, the study identifies a flexible core of documentation fields for 3D cultural heritage in the context of data aggregation. The paper proposes a tiered model of metadata necessity and highlights the importance of transparency in modeling methods, authenticity, and provenance. Recommendations are designed to support both aggregation and domain-specific needs, promoting better access and sustainability of 3D cultural heritage data across institutional repositories and research environments.