Here's another of those articles Arthurian fans in our ranks either love or hate. It has studies of language and studies of poetry (one French example is very crude - where's the courtoisie in that, you might ask) to examine the dating of Nennius' battle list.
King Arthur and the Origin of Bardic Verse
Bernard Mees
https://muse.jhu.edu/article/994760
Thank you...I think ;D