I appreciate your thorough analysis.
In R 1,29, however, the Alexandrian MS 81 (11th c.), which the Alands
categorize as "at least category II," does in fact omit FONOU, if I
read von Soden correctly here. In the same verse, A/02 omits DOLOU
after the transposition of FONOU ERIDOS, making h.t. error in both
cases the likely cause. Also in R 1,29, there is the omission of
PONHRIA by K (and 1912 acc. to von Soden?), and PONHRIA PLEONEXIA by
1836, again, acc. to von Soden(?). Here is also a famous case for
conflation by Byz in reading both PORNEIA (Ds* G [P]) and PONHRIA,
but even here I'm sure M. Robinson would vigorously defend PORNEIA on
grounds of h.t. error exemplified by similar scribal habits in the
Back to G 5,21: you are very clear that the issue revolves around the
"likely borrowing from the parallel, the improbability of deletion,
the penchant for a fuller text."
I have a basic question: Can the h.t. habits of a scribe (or
scribes) in any century (especially late centuries) be used to argue
against the reading of the three oldest MSS we have for G 5,21? If
so, under what guidelines?