More precisely, it would be interesting to understand,
–whether there is at all the feeling of the need of literal quotations.
–whether literal quotations are explicitly marked (at least as a rule) by, e.g., iti vacanāt or similar expressions.
–whether non-literal quotations are marked (at least more often than not) by, e.g., iti manyate or similar expressions.
–whether literal quotations are more often than non-literal ones marked as such (at least by iti) and, if so, if their source is also mentioned.
–which kinds of texts are literally quoted (sacred texts? texts by revered teachers? adversaries' ones? texts the readership is expected to know and would hence be disturbed to find changed? texts the readership is not expected to know and hence needs to be acquainted with?)?
–are iti śruti, iti smṛti, iti prasiddha, iti dṛṣṭa, iti āmnāta and similar indications reliable?
The more technical side of these questions (that is, frequency and number of quotations and their marks) would be better answered through a certain amount of case-studies in as far as possible different fields of Indian philosophy. In fact, I suspect that traditions more closely linked to writing might have developed different habits from ones still 'suspicious' about the written form of a text. This pre-judice is however in need of confirmation.