A lot seem to be happening on RG and a lot of academics get to visit other people's work or access electronic documents from others. We need to clearly follow the academic criteria by acknowledging the sources from which we collect our information
Yes it's important to acknowledge references cited by an author in an article it wouldn't be enough to cite the other of a new article constructed from the works of others so for instance if it was something I wrote and I cited your article I wold have to give you an acknowledgment for your article. If someone then used my citation of you work and I had made a reference or an analogy that disagreed I to would be includerld so the reference would also mention my name as the person who cited your work recognising each person's input is crucial if we don't want someone vexed by theft of property or ideas first developed by someone else. I should think that if everyone recognises each other's contributions this would not be an issue I agree it's difficult and I am sure no one would breach codes of referencing or the ethics around someone else's research property but it could happen. Possibly only recourse would be to approach individuals institution with a grievancy or to investigate. An interesting question but one I would have thought individual institution would have put policies in place to control and prevent then again anything's possible.
Intellectual property rights are normally territory based. This means to say the protection is not world-wide but limited to the countries where the rights have been registered. Registration is normally available for patents, trade marks and industrial designs to name a few. However, copyright has no such registration requirements. It comes into existence the moment the work is created.
Infringement of copyrights is a serious matter to be reckoned with.
The question to me seems to be two fold:
1. Copyright gives the author exclusive rights to exploit the expression of his work as he /she deems it appropriate. When such work is incorporated in the work of the other due acknowledgement needs to be given.
The amount of work taken, is normally the issue before the courts. If the work has been substantially copied and there is no real difference between the original work and the later one, this will be deemed to be an infringement of copyright.
However, sharing of work for academic purposes falls within the exception - each is catered for in the local copyrights act.
2. Where the information is incorporated in the work of the other, academic integrity warrants that it should be referenced in accordance to the recognised protocols of referencing.
I do not know whether I have answered the question but these are my thoughts.