Without implementing https://jira.nypl.org/browse/SIMPLY-2631, making network caching improvements on iOS is a screen-by-screen process. This ticket describes the two HTTP requests where respecting the Cache-Control header is most important:

1. The request to the library registry for the list of libraries. This request might go to one of two specific URLs: https://libraryregistry.librarysimplified.org/libraries or https://libraryregistry.librarysimplified.org/libraries/qa
2. The request for a circulation manager's authentication document. You'll find this URL inside the document you get back from the library registry. It's kept in a link with type="application/vnd.opds.authentication.v1.0+json" and the URL typically looks like this: http://acl.simplye-ca.org/CALMDA/authentication_document

If you don't get a Cache-Control header for one of these documents, then cache the document for three hours.