[Facts] Re: Maria, Mariam and Marian
I don't understand your comment about "it is the job of textual criticism to wipe out such errors." There weren't "textual critics" back in the 4th century. If the mistake was made before the creation of the earliest copies that are still in existence, it would still be in the text we have. Textual critics don't change the printed Greek text unless they have alternate written sources. I would also assume that many literate people in New Testament times would know both Greek and Latin, so it seems perfectly reasonable to me that knowing Latin could influence the sort of name forms or variations one would come up with in a Greek manuscript of the time.
But the only sources I have for the Latin accusative case theory are name dictionaries. What you need here is to consult someone who is a Biblical scholar who is very familiar with New Testament Greek.