If you only look at the Smartlist, then you only see files with something in the Link field. However, if you play the Smartlist, then all linked files, including the last one, are added to Playing Now.
Once you have the entire list in Playing Now, you can create a new tag (if necessary) called Linked Files and fill that tag. Create a new Smartlist based on that tag and you will see all linked files. If you ever unlink files, though, you would need to retag your custom tag. I would just view and work with the files in Playing Now.
