Is it sufficient that there are previous books that dealt with the same research, with a slight difference, or must the research be completed? And is the work attributed to the researcher or to the authors of the previous books?

Copyrights and intellectual property rights are private rights belonging to their owners, recognized as legitimate in Islamic law, and it is not permissible to infringe upon them. If what was written consists purely of the author's own ideas and efforts, without infringing on anyone else's works, then there is no harm in completing it, benefiting from it, and attributing it to him, even if it is later discovered that someone else preceded him on the same topic. This is because, in such a case, it is merely a convergence of ideas, provided there is a significant difference in style or ideas. It is advisable to mention in the introduction the existence of other research on the same topic. It is not permissible to attribute the work to the authors of previous classifications.