Abstract: Systems and methods are provided for efficient post-processing of object-based snapshots of block-storage volumes, which post-processing may include garbage collection, validation, or resource usage auditing for the snapshots. An object-based snapshot can be logically represented by a set of objects stored on an object storage service, which objects collectively represent a copy of the data of a corresponding block-storage volume at a given point in time. Each snapshot can further be represented by a full manifest that includes a full listing the set of objects representing the block-storage volume, and a differential manifest that includes a listing of objects unique to the snapshot relative to a prior snapshot of the same volume. Full manifests enable each snapshot to remain independently represented, while differential manifests enable efficient post-processing by reducing the amount of data retrieved and processed to identify an aggregate of all objects referenced across a group of snapshots.