One of the problems in recognising a marked quotation is that it might be marked just by an iti. However, iti can also indicate just the end of an objection, even a longer one. So, the more general question arises: Do we have to consider objectors in Indian philosophical texts to be historical figures or not? Have their thoughts been reproduced from other texts or rather invented by the author of the text one is examining? The two questions are not mutually exclusive insofar as we know of objectors which were (no longer?) historical figures, but whose views have been reproduced from text to text (on this theme, see also my previous post on the subject of the "heretic" in Tibetan literature), such as many Lokāyatas.
Conforming to my intention to read more (see), I tried to find out what has been written on these themes. I will add my next discoveries here. For the time being, I can only mention Emery R. Boose's chapters on iti and on references in Gary A. Tubb, Emery R. Boose, Scholastic Sanskrit, Treasury of the Indic Sciences Series, AIBS, New York 2007. The book is great in concept, but it is still very basic in its indications (at least in this case).