In this scenario, a large number of .mbox files were being discovered and converted to PST files. The discovery job was stopped and restarted, followed by a successful processing job.
The concern was that Case Status page still showed 'Pre-Processing - Discovery and Scanning' job as stopped. There was a need to verify that the processing job processed all .mbox files.
Select the source and run 'Discover new files for source followed by 'Start processing source w/o Discovery'.
This will ensure that all Mbox files were processed and converted to PST's, in situations where a Discovery job was deliberately stopped.