I have been arguing in several older posts (see: 1, 2, 3, 4) that in Indian philosophical texts the concepts of "copyright" and, consequently, of "plagiarism", lack. . Everyone copies, better, everyone uses his predecessors words and conclusions as building blocs (Bausteine) for one's own work. Why, then, are authors so frequently recorded in Indian philosophical texts? Many, possibly most, philosophical texts are said (either in the mangala or in the colophon) to be "the work of...". Moreover, authoriality is a big issue whenever it refers to past and well-known authors, such as the author of one's school foundational text, Vyāsa, etc. It is so even in schools -like Mimamsā- which maintain the independence from an author of the Veda.
The apparent contradiction may possibly be solved if one considers that "author" and "authoriality" do not share the same meaning in classical Indian philosophy and contemporary enquiries. The author could have been felt, in the first one, as a pra-vaktr, that is as "an excellent upholder" of the school's ideas. Kumārila and Jayanta Bhatta seem to have been seen and to have understood themselves as such.
The situation is different in case of semi-divine authors, such as the Vedic rsis, Gautama within the Nyaya school, Kapila, etc.). They are of foundational importance because they are endowed with an epistemological faculty to ground what they say, through intellectual intuition (yogipratyaksa). Some schools, such as Mimamsa, deny any validity to yogipratyaksa. But even the ones which acknowledge such possibility for some extraordinary human beings, do not rely on it for the successive history of the school. Hence, a first authorial foundation is useful to ground -through the yogipratyaksa faculty of an extraordinary human being- the validity of the whole system. But thereafter the system is developed through a succession of authors and commentators who are nothing more than the voices expressing the school's ideas.