The Digital Repository Service (DSR) at Harvard Library has the highest level of PREMIS conformance, by the following guidelines:
"18.4.3.2 Level 3B: Object, Event and Agent Entities
A repository implements the PREMIS Data Dictionary as an internal metadata schema in a way that satisfies the principles of use at both the semantic unit and Data Dictionary levels and in a form that does not require further mapping or conversion. The repository implements, at a minimum, the Object entity; one or more Agents; and sufficient Event metadata to document actions the repository has taken to preserve the digital objects."
"While we would not describe Level 3 as the 'top level,' it is the 'purest' level in terms of PREMIS. It requires institutions to record metadata using absolute PREMIS terms. There is no mapping as the elements are named exactly the same and the optionality and repeatability are no less stringent."
"This 'B' subcategory expands the number of entities required to be conformant to include Agents and Events. These were felt to be the most crucial of the remaining entities required to be conformant as they note what actions have been undertaken to preserved objects and who or what carried out that action. In essence, they help maintain the integrity of the preserved object. The Rights entity is deliberately not part of either subcategory. Experience has shown that there are many other ways of capturing rights information, whereas for the other entities, PREMIS is the primary expression of the required metadata."
McKinney, P. (2016). Conformance with PREMIS. In Digital preservation metadata for practitioners: implementing PREMIS (pp. 251-252). Switzerland: Springer.