Funny thing about the oldest known manuscript of John's Gospel. The scribe who wrote down what we now call Papyrus Bodmer II, or more lovingly P66, seems to have been a careless type, prone to screw-ups and self-corrections, as many as 450 of them. One such self-correction -- if that is what it is -- appears at 11:1, where the words "There was a certain sick man, Lazarus of Bethany, the village of Mary and of Mary his sister" have been corrected to the more familiar "... the village of Mary and of Martha her sister."
Looking at the manuscript, a reader can actually see where the iota has been scratched out and a theta added as a superscript, changing marias to marthas.
The latter thesis is is argued by Elizabeth Schrader Polczer in her paper ,"Was Martha of Bethany Added to the Fourth Gospel in the Second Century," in Harvard Theological Review 110:3 (2107), pp. 360-392. You can hear her non-technical, and very entertaining, discussion of the idea in a recent (2024) podcast with Dave Roos and Helen Bond, at Biblical Time Machine.
Polczer's argument does not by any means hang on this single cut-and-paste. She looks at a range of manuscript witnesses to John, notably Codex Alexandrinus but also many other, both Greek and early Latin, and finds that Martha's presence is "unstable." Sometimes she appears in John 11 & 12, sometimes she does not; sometimes the grammar suggests one sister, sometimes two. So persistent is the confusion that traces can be found in Tyndale and even first printing of the KJV.
Her suggestion is that the earliest scribes faced a dilemma of some sort. Perhaps there was an earlier text of John in circulation, which did not feature Martha, or which featured her isn a smaller role. and they felt a need either to bring her in or to enhance her position. Indeed, source critics, such as Bultmann, Fortna, and many others, have often suggested something like without much reference to the textual history.
But if such an ur-John existed, why add or magnify Martha? Merely to identify John's Mary the sister of Lazarus with Luke's Mary the sister of Martha? Or to make a theological point by doing so?
We won't hold you in suspense. Polczer suggests, tentatively, that the objective was to separate in readers' minds the Mary of John 11 and the Mary of John 20, "where one woman named Mary also cries and speaks with Jesus at another tomb." In other words, she proposes a more-or-less concerted effort to reduce the prominence of Mary Magdalene in the Fourth Gospel. If so, this was ultimately accomplished "by dividing one woman into three," that is, into Mary Magdalene, Mary of Bethany, and Martha.
("But wait," you cry. "Bethany is one town, and Magdala another. How can she come from both?" Briefly, there is, and always has been, a strong case that John's epithet "called Magdalene" refers not to a particular village, but to a nickname derived from the Aramaic migdal, or "tower." As Cephas and the Boanerges testify, Jesus liked to give his followers nicknames.)
If this is true, what was the theological objective of the Magdalene-minimizers? Polczer's paper stops short of a clear proposal, although in the podcast she and the hosts engage in some banter about the Peter-o-philes, meaning Christians who wanted to depict Peter as the primary heir to Jesus' authority. That such a faction existed in the early Church is clear, although offhand we can't think of evidence for it as early as 200 CE, the rough date of P66.
None of this is certain, but Polczer has many sources, and her thesis is interesting. It does indeed suggest a possibility to which we were exposed, in a passing comment by a seminary professor many years ago, that the New Testament as we have received it shows signs of selective editing around the ministries of certain critical figures -- Peter and Paul, obviously, but also John the Baptist and Mary Magdalene.