One of the main accusations against Simonides can be seen here:

Journal of Sacred Literature
https://books.google.com/books?id=vvgDAAAAQAAJ&pg=PA484

Now, we can well understand and acquiesce in the appropriateness of such a gift, made by a body of religious men, to one whom they regard as the head of the Church to which they belong. And, that Church being the Greek Church, we can appreciate their good taste in having the MS. written in the Greek language, and in Greek characters. Moreover that the oldest style of character should be used; that the writing should be on vellum or parchment, according to the ancient practice of the church. All such particulars legitimately attach themselves to a perfect renaissance, which it would seem it was intended this MS. should be. But when we are told that the colour of the ink (a faded one doubtless) on the most ancient MSS. was carefully matched; that bone pens were made, and the hue of the skins imitated ; and of course every little peculiarity of letter affected, so that the minutest evidence of antiquity might not be wanting;—I say, on all these accounts, and many others of a like kind, there does appear to be prima facie evidence of an intention to deceive, to cozen, to trick into a belief in the existence of something which had none.
This shifted the question away from who actually wrote the manuscript to the question of whether the motives of Simonides and crew were crystal clean.

This is an absurd shift, and ends up trying to avoid the actual question.

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From the point of view of SImonides and Kalliinikos, at some point it was rejected as a final version, and thought of more as a draft copy. That would explain anomalies like small letters in margin writings, accent scrawls, Arabic scribbles and more.