Your local catalog should have retained items denoted in some fashion. Local practices may vary, but at a minimum a 583 field in a bib, holdings or item record should be present in retained materials.
You can also see what is listed as retained in OCLC Record Manager by following their instructions for Shared Print LHR searching.
Retentions are also listed in Gold Rush, and based on exports from your local system. If you need a list of records which were deposited into Gold Rush, contact us at info@eastlibraries.org and we can assist you with a login and instructions to retrieve the records.