The story traditionally printed as John 7:53-8:11 has been read and cherished in the church for centuries. At the same time, its textual history differs markedly from most passages in John's Gospel.
Modern readers benefit from knowing both facts rather than having either one concealed.
Important early Greek manuscripts of John do not contain the passage, and several early witnesses move directly from John 7:52 to 8:12. In later manuscript traditions the story appears in more than one location, including after John 7:52 and, in some witnesses, elsewhere in John or Luke. These features are strong evidence that it was not originally located here in the earliest form of John's Gospel.
The story itself is ancient and was known in the early church, so textual uncertainty about its placement is not the same as proving that the event never occurred.
The manuscript evidence encourages careful confidence rather than alarm. Ancient copying preserved enough evidence for readers to see that this passage has a different transmission history.
For interpretation, it is wise to distinguish the historical and pastoral value of the ancient story from claims that depend upon proving it belonged to John's original text at this exact location.