We are conducting a new research project to improve the global understanding of repository content by generating yearly statistics on research materials held by repositories. The project will assess the volume of undiscoverable content, estimate the number of repositories that are not registered in public repository registries, and differentiate scholarly resources deposited directly in repositories from those merely linked. It will also consider issues of duplication and multiple versions, such as preprints and postprints, to produce statistics that can be easily interpreted. This work complements and extends existing Open Access monitoring efforts by including content that both contains and lacks persistent identifiers (PIDs), taking into account an estimated 100m+ scholarly records that usually go untracked. Ultimately, the project aims to build an infrastructure for better monitoring and understanding of repositories' roles in scholarly communication, facilitating future research into Open Access growth.