Are there pages listing links specifically to original works by NWC users? There must be more original compositions other than those shown by the links on the Registered Users' Music Pages (http://www.noteworthysoftware.com/composer/userlinks.htm).
The Noteworthy Scriptorium, which heads the list on the link you pointed to, in fact has over 8000 files. Many, many of those are original works by Noteworthy users as well as non-copyright transcriptions of pieces by well known composers.
You can look up music by a particular composer by visiting The Composer index (http://nwc-scriptorium.org/composer.html)
You will be able to see if the composer is a Noteworthy user by inspecting the dates in the index.