I have little to add to the most interesting thread you have begun, but I do wish to call your attention
to a recent article that may be of interest in that it presents an analogous problem of a
manuscript whose different parts yield highly divergent C-14 dates:
Amy Heller, "Three Ancient Manuscripts from Tholing in the Tucci Collection,
IsIAO, Roma. Part I: Manuscript 1329 E," in STUDIES IN HONOUR OF LUCIANO PETECH, Roma 2016.
In this case, it is a question of a Tibetan ms., some of whose parts yield an 11th c. dating and others 16th c.
Ecole Pratique des Hautes Etudes
Numata Visiting Professor of Buddhist Studies,
The University of Chicago