If you are saying that something is an external DTD subset only because 
it is referenced as such from a document entity, you are certainly correct.
As an extreme case, consider a file containing a single comment.  It can 
become an external DTD subset, external parameter entitiy, or external 
parsed entity, if it is referenced as such.
Makoto
 
Fuji Xerox Information Systems
 
Tel: +81-44-812-7230   Fax: +81-44-812-7231
E-mail: murata@apsdc.ksp.fujixerox.co.jp