OE Fethuir

Sorry to drag up an old post, but I wanted to ask another question...

Nennius, in the Historia Brittonum, chap 17, mentions an individual by the name of "Fethuir". I find the name spelled that way in modern English translations such as at www.fordham.edu/halsall/basis/nennius-full.html
I also find the name given that way in Keith Fitzpatrick-Matthews's reconstructed Latin version of the original text at www.kmatthews.org.uk/history/hb/historia_brittonum5.html#m17
Whereas in the Latin version by Theodore Mommsen, the name is given as "Fetebir".

I had previously asked whether Fethuir/Fetebir was cognate with modern English "father".
Brian M. Scott, thoughtfully replied that the proper OE was <fæder>, and that the change from [d] to [ð] did not occur until the Middle Ages.

Recently I was re-reading some notes which included David Dumville's assertion that the Historia was continually modified until the 12th century.
At what time did the exact switch from d to "eth" happen?

Also I am curious what is to be made of the Latin "Fetebir", and how does that affect any possible cognate with "father"?


As always, any help would mean a great deal!
Sincerely,
Aydan