I am summarizing a course overview note which includes some useful information about digital marketing. The thing is, there's a endnote that clearly says that the course was prepared by professor X and professor Y. However, another endnote says that this 'course overview note' (the note itself) was prepared by professor Z. There are no citations in the note except for further suggested readings and a few explicit ones.
So when I am summarizing the ideas, should I cite them as: (Professor Z 2013) or always refer to (Professor X & Professor Y 2013)? Note that I, obviously, don't have access to the original course material itself.
Edit: Author of the note says: 'while maintaining many concepts and cases, this note provides an alternative structure and view of the set of frameworks to their original course'. However, it isn't clear where his ideas start and end, and where their original ideas do so.