I think your information is a litle out of date since there seems to be some general agreement that the “pericope” story seems to have been well know to the churches as far back as 2nd century AD. Even then, there was some controversey back then as to whether it was truly of John or not... or whether the story belonged in some other writing but was sort of “stuck” in John. Again, I think it comes down to personal conviction and belief as to whether the early church fathers felt it was truly “God breathed or not.
{”Jerome reports that the pericope adulterae was to be found in its canonical place in “many Greek and Latin manuscripts” in Rome and the Latin West in the late 4th Century. This is confirmed by the consensus of Latin Fathers of the 4th and 5th Centuries CE; including Ambrose, and Augustine. The latter claimed that the passage may have been improperly excluded from some manuscripts in order to avoid the impression that Christ had sanctioned adultery:
“Certain persons of little faith, or rather enemies of the true faith, fearing, I suppose, lest their wives should be given impunity in sinning, removed from their manuscripts the Lord’s act of forgiveness toward the adulteress, as if he who had said, Sin no more, had granted permission to sin.”}
The Pericope controversey seems to have been raised to a fevered pitch in more modern times. (Beginning with Lachmann (in Germany, 1840), reservations about the pericope became more strongly argued in the modern period, and these opinions were carried into the English world by Samuel Davidson (1848–1851), Tregelles (1862), and others; the argument against the verses being given body and final expression in Hort (1886). Those opposing the authenticity of the verses as part of John are represented in the 20th century by men like Cadbury (1917), Colwell (1935), and Metzger (1971).) However, this is hardly surprising since this was the time period that all historical assumptions about history and Christianity were to be put under the deconstructionist microscope. It is also the same time period that progressivism, marxism and fascism arose using many of the same “deconstructionist arguements” questioning the Bible and the existence of God as part of their own modus operandi.
So much for your view that some “nut added” the story some 1500 years later; the real nuts who seem to have been most strident against the Bible accuracy of this story have been certain “researchers” from the last 2 centuries or so!
Yes, it found its way into the Vulgate, notorious mostly for being unreliable. The fact is the oldest, reliable Greek manuscripts and Codices don't have it. This is the same Jerome who insisted on using the Pharisaical version of the OT despite the fact that the Apostle overwhelmingly used the Septuagint.
Somewhere you mention Papias (2nd century), another very unreliable source. We "know" about the Gospel authors mainly through him, and he heard it basically from people (in other words, tales and hearsay). Eusebius (late 3rd cent.), the first Church historian, calls Papias "dimwitted."
In other words, one never knows where things that are in the Bible came from. But some people take it "on faith," as you say. Right on.
And since you are apt at Goggling verbatim the information without even mentioning the source, you may wish to check on another biblical fraud otherwise known as the Comma Johanneum. It's another example of a religious nut playing God. But that doesn't stop Bible-worshiping individuals from quoting them as the "Word of God."