...
SP provides mechanisms to ensure that the content held in the repository remains uncorrupted through the use of regular fixity checks. See XXXXXXXXX Fixity Check Procedures.
While SP has a record and can generate a list of everything it has in the repositiry, the repository can only ingest the content that a Provider chooses to send. It is difficult to know whether or not this represents the entirety of the collection without a complete list to check it against. These gaps can be identified through feedback from the Designated Community. Additionally, SP supports and is involved with the Keepers Registry in order to help create a central registry of scholarly journal content.
...
See TRAC items 4.2.1 - 4.2.4 and 4.1.8