Dave Black had some interesting notes on this subject today, which I posted to The Jesus Paradigm. There is a constant debate on what is “correct” usage. We have this with regard to modern usage. I’ll have authors cite some manual against their editor, usually on optional items.
So why do we expect all usage to be equal in Koine Greek?
Here’s Dave’s money quote, I think:
Lately it’s become clear to me that the question concerning correctness and incorrectness in language is not so much a linguistic one but a sociolinguistic one. In other words, it is people who determine what is correct and incorrect in language, not textbooks. In a sense, then, if everybody says “It’s me,” then this construction is correct.