So, let's get down to the nitty-gritty here.
Up until about 1,000 years ago, no version of the Bible included the passage about the stoning. ("Let he who is without sin throw the first stone, etc.)
During the 1,000 years before it's spontaneous appearence in the Holy and Unchanging Bible which was written by men directed by God so they can't possibly have made any mistakes, no Biblical scholar made any mention of the passage. So it's safe to assume that there isn't some Biblical Missing-Link that we just haven't recovered.
Basically, 1,000 years ago someone said -- "Hey, this sounds like something Jesus would say." and added to the Bible. At that point it went immediately from "Something Jesus would say" to "Something Jesus DID say."
That's 1 account of an addition. How many more are they? How many deletions? How many more additions are to come?