Was 'Jesus and the woman taken in adultery' in St. John a later addition, and does this invalidate infallibility? In John 7:53-8:11 we have the account of 'Jesus and the woman taken in adultery'


  53 Then they all went home, 1 but Jesus went to the Mount of Olives. 2 At dawn he appeared again in the temple courts, where all the people gathered around him, and he sat down to teach them. 3 The teachers of the law and the Pharisees brought in a woman caught in adultery. They made her stand before the group 4 and said to Jesus, “Teacher, this woman was caught in the act of adultery. 5 In the Law Moses commanded us to stone such women. Now what do you say?” 6 They were using this question as a trap, in order to have a basis for accusing him. But Jesus bent down and started to write on the ground with his finger. 7 When they kept on questioning him, he straightened up and said to them, “Let any one of you who is without sin be the first to throw a stone at her.” 8 Again he stooped down and wrote on the ground. 9 At this, those who heard began to go away one at a time, the older ones first, until only Jesus was left, with the woman still standing there. 10 Jesus straightened up and asked her, “Woman, where are they? Has no one condemned you?” 11 “No one, sir,” she said. “Then neither do I condemn you,” Jesus declared. “Go now and leave your life of sin.”


Many modern translation include notes like this one (NIV).


  "The earliest manuscripts and many other ancient witnesses do not have John 7:53—8:11. A few manuscripts include these verses, wholly or in part, after John 7:36, John 21:25, Luke 21:38 or Luke 24:53."


And some translations print the entire passage in italics to indicate that it is most probably not an original passage. 

Read this article for more full explanation for and against. 

My question is if this is a later addition then what implications does this have? Does is invalidate biblical infallibility? Does it change any moral or religious applications to this passage?
Forgive me for answering my own question…

There are several scenarios I can think of regarding this passage.


John himself added this passage later on.
John told this story enough that later his followers thought it appropriate to add this passage to John’s account.
This account was so common among early Christians and fit so well at this point in John’s gospel that the early Christians felt is appropriate to add this story here. 
John himself had written this account elsewhere, and his followers later combined it with the rest of his Gospel. 


If any of these explanations are true, or something similar happened, it would not invalidate the truth of the account historically, or otherwise. Likewise, just because the very earliest manuscripts do not contain these words exactly it does not necessarily follow that it is not true or any less inspired.