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.