not looked in detail at your example, just perhaps just answering this
bit iis enough

>  I am familiar with keys and get get lists of unigue items and group
>  them but I cannot exclude the items that do not appear in all
>  StudyGroups...  

one way

<xsl:key name="sg" match="studyroup" use="item"/>

then <xsl:variable name="n" select="count(studygroup)"/>

so to know if . the current item is in all groups you can test 
count(key('sg',.))=$n
as if it is in all groups then the key will return them all

David


________________________________________________________________________
The Numerical Algorithms Group Ltd is a company registered in England
and Wales with company number 1249803. The registered office is:
Wilkinson House, Jordan Hill Road, Oxford OX2 8DR, United Kingdom.

This e-mail has been scanned for all viruses by Star. The service is
powered by MessageLabs. 
________________________________________________________________________