Identifying quotations and making readers aware of them

As many readers know (for newcomers, see here), I am deeply interested in the topic of the re-usal of previous textual materials by Indian authors and hope to be able to collect essays dealing with case studies of this usage in various śāstras. A further output of the project should be the elaboration of a common way to mark re-used textual materials. Until now, such materials are often marked in different ways according to the scholars identifying them (e.g. with "cf." or "=" or just the indication of the source). Ernst Steinkellner (Methodological Remarks on the Constitution of Sanskrit Texts from the Buddhist Pramāṇa-Tradition, WZKS 1988) elaborated a proposal for their classification (using symbols such as Ce, Cee, Re), but his method did not gain general acceptance and it has been criticised by many scholars because of its evaluative character. In fact, saying that a certain author, e.g., Kumārila, has "cited" a passage "out of" a certain work, e.g., Dignāga's Pramāṇasamuccaya (Ce) implies that Kumārila was aware of what he was doing. However, it is often the case that an author cites by hearsay, or that both the attestations of the passage drive from a third, unknown source. Last, chronology is far from being settled in Indian philosophy and it is likely the case that we will find out that, e.g., it is not Dharmakīrti who quoted from Bhāvya but rather the opposite. And everything gets even more complicated while dealing with anonymous texts, apographs or religious texts. These latter texts, in fact, extensively re-use previous ones but are often themselves the result of several generations of "authors". More generally, the judgement about who quoted whom is in fact in many cases less smooth than at first sight expected.