Indexable documents are documents with states from enabled workflow input states. The Web.config option AllowAccessToDocumentsToIndexOnly and the Web Verifier option Disable navigation to valid documents control the navigation to indexable documents.
Example
Workflow settings: 550 -> 700
A batch includes documents with states 550, 600, and 700.
If you set AllowAccessToDocumentsToIndexOnly to True and activate the Disable navigation to valid documents option in Web Verifier, you cannot access documents with state 600 or 700.