In "Archaic Mark," a.k.a. 2427 in the NA-27 apparatus, the forger skipped a few words which were presented within parentheses in Buttmann's printed NTG. Somehow, he must've misunderstood the significance of the parentheses, as if they meant that the words within them were not part of the text.
I wonder if copyists ever made similar mistakes involving parenthetical phrases. They might not actually see parentheses on their exemplars, but something like parentheses -- maybe non-standardized punctuation of some sort -- might provoke a copyist to misinterpret a parenthetical phrase as if it is secondary.
In Mt. 10:3, Thaddaeus is just plain Thaddaeus in the Alexandrian text, but he's Lebbaeus in the Western text, and he's Lebbaeus who was surnamed Thaddaeus in the Byzantine Text. (And there are other variants, too; several OL support "Judas Zelotes". 13 and 828 have "Thaddaeus who was surnamed Lebbaeus.") Metzger accounted for the Byzantine reading as a conflation, although if the Byzantine reading here is secondary, then it's not a simple conflation of the Alexandrian and Western readings; the words "hO EPIKLHQEIS" must be imported.
What if the reading in D is just one more messed-up Western reading , and the Alexandrian reading -- if not the result of a simple h.t.-elicited error from -AIOS to -AIOS -- originated when a copyist saw unclear punctuation in his exemplar, interpreted "who was surnamed Lebbaeus" as a parenthetical phrase, and did not perpetuate it? The reading "Thaddaeus" would be the result.
Perhaps the non-inclusion of Jairus' name in D (Mk. 5:22) can be explained by the same theory.
Yours in Christ,
James Snapp, Jr.