“The Epistle of Barnabas (c. 100 AD) and Shepherd of Hermas (c. 100 AD) are apocryphal texts present in both the Codex Sinaiticus and Codex Alexandrinus.”
They are not present in Codex Alexandrinus.
Hermas is partially extant in Sinaiticus, approximately 30% was in the Tischendorf loot of 1859, and a smaller pct. added in the New Finds of 1975, towards the back end.
As for the Sinaiticus text of both books, world-class Scottish scholar James Donaldson (1831-1915) wrote about their texts in 1864 through 1877, saying that the Latinization elements pointed to a much later date, at least centuries later, than the 300s “consensus” date for Sinaiticus.
(Ironically, this developed out of a Tischendorf attack on the very similar Hermas text of Constantine Simonides of 1855 as including Latin retro-version elements. Today the Simonides text is known as Codex Athous Grigoriou 96).
Some of the Donaldson examples have been disputed. However, his overall argument has never been given deep examination. Today, few scholars really have the Greek and Latin, Hermas and Barnabas skills that would be required.
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There is another issue that was raised because of the "coincidence" of the Constantine Simonides Greek Hermas being published just a few years before the Sinaiticus discovery, (Until this time there had been no Greek Hermas.)
James Anson Farrer in Literary Forgeries (1907) p. 59-60 Greek Forgery: Constantine Simonides
"That Simonides was a good enough calligrapher, even at an early age, to have written the Codex, is hardly open to doubt, and it is in his favour that the world was first indebted to him in 1856 for the opening chapters in Greek of the Shepherd of Hermas, with a portion of which the Codex Sinaiticus actually terminates. The coincidence seems almost more singular than can be accounted for by chance."
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In other words, we should consider the possibility that Mt. Athos and Simonides were involved in the production of the Sinaiticus Hermas in the 1800s, in which case they were involved in the full Sinaiticus.
It is all rather fascinating!