I still think it would take a couple of years of research and a few
hundred pages of write-up to do justice to the question of when,
where, how and by whom these texts were composed and redacted.
But the picture I have in my mind -- and this is only a possibility,
I cannot here muster arguments in support of it -- is that there were
some monks who remembered the early teachings quite separately from
the "mainstreamers" who put together the Nikaaya-s. Monks like our
friend Kondañña who had some brief contact with the Buddha early on,
and then went their own way, never becoming involved in the communal
life of the "Sangha" as "assembly."
But I do emphasize that I don't think we can do justice to this topic
in a few minutes of e-mail.
Even a simple question like the dating of the Niddesa would take some
effort to go into. I am just quoting from von Hinueber here, but
apparently S. Lévi devoted 55 pages to a study of the Niddesa, and
arrived at the surprisingly late date for it of the 2nd century AD.
And then of course, there are the counter-arguments for an earlier
date -- K. R. Norman puts it at the time of A"soka. Von Hinueber
concludes: "This question needs reexamination."