Here are the SharePoint workflow status codes which you can reference in SharePoint to filter your list/library view or use them in the workflow itself.
I think the numbers between 8-14 are reserved only for SharePoints internal use.
If you start the workflow for the first time, it will create automatically a new column with the workflowname, in which it then inserts the appropriate codes above. You can see this by opening the library in the DataSheet view:
This workflow status column is now also shown as part of the view. So you can filter for it by entering one of the status codes above (not the text).
Another possible scenario would be to use the codes in one of the workflow actions directly, for instance in Nintex Workflow Actions: