Is this unprofessional academic writing? How to cite it anyway? I am currently preparing some case studies written by Harvard Business School professors. The case is a 'real marketing' case; based on a true story. It is mostly compiled from many sources such as newspaper articles and books. Aside from common knowledge, the authors sometimes provide information (i.e. factual) without any reference, other times they do. I, sometimes, try to 'find' an original source for their un-referenced claims (and always track the referenced ones).

My question: If I don't bother to find a primary source by myself and simply cite the case writers for the information they are presenting (the ones without references), is this a bad practice? Is it plagiarism? (Since the information could have belonged to someone else)

One more thing I noticed which is really confusing is that, sometimes, the authors write an idea without a reference and then, by accident, I discover that such an information belonged to reference #24 (for example) which is like 5 pages away (How did I discover it? By tracking the reference #24 and reading it and discovering that this information is the same presented in page 1 for example (which was without a reference))! How should I handle such a situation? Can I, again, simply cite the authors for whatever un-referenced information they are presenting? (Assuming that they are HBS professors and know what they're doing)

I am just worried about plagiarism and crediting the wrong people.
If you cite the secondary source (the book written by the sort-of-careless Harvard professors), you are not at risk of plagiarism.  That does not mean it is great practice: finding a primary source or something close to it is always a good idea.  But you will not be at fault if you simply site the Harvard profs and take them at face value.

One thing you could do is find secondary "primary" sources to back up the profs.  Then you could site an idea like this:


  ... and that is why monkeys like to steal bananas from the Harvard library (Mr. Fancy Harvard Prof 1, Mr. Fancy Harvard Prof 2, 1999) (Mr. Honest Zoo-Keaper Who Interned at Harvard, 1998).


Wherein the "Mr. Honest Zoo-Keaper Who Interned at Harvard" is the primary source you found on your own, externally, who seems to back up the less-than-well-documented assertions of the illustrious "Mr. Fancy Harvard Prof 1" and "Mr. Fancy Harvard Prof 2".