@liminal my point was that the 30040's have two uses. On the top level they are used as a book. On the second and deeper levels they are used as sections. 

Imagine there are thousands of books and tens of thousands of sections (all 30040 events).  How do I query for the list of books? IMHO there is a tag needed to identify the top level books. 

 I agree a distinguishing tag would be useful. 

Top-level 30040s *should* have no e tags, but they definitely *must* have the top-level tag.