AP: Well, what you've written in your question is true. In general, the fourth Gospel is more so a theological interpretation of Jesus by its redactors. Here are the main points:
The duration of Jesus' public ministry lasted two or three years. John says there were three Passovers, while the Synoptics say there was only one.
Jesus began competing with John the Baptist, baptizing people in the Jordan. He founded his own group and dragged away some of those disciples.
There are doubts regarding the interpretation of the Last Supper, which is not mentioned in the fourth Gospel.
There are serious doubts about whether there were two gatherings of the Sanhedrin to condemn Jesus, or just one. Did the one take place earlier in Jesus' ministry? For example, we see in John 11 that Caiaphas had already determined that he had to die.
There are doubts concerning the date of Jesus' death. It was definitely a Friday, as the Synoptic accounts tell us. But was the Friday of the actual Passover, which began in the afternoon, or was Friday the "preparation day" of the Passover?
There are doubts concerning to whom Jesus first "appeared." Was it to the women? Was it to Mary Magdalene?There's lots to think about here.
TWH: There is so much literature out there concerning this issue. Lots and lots of material that you can sift through. There's no question about it. I just flipped through Marianne Meye Thompson's chapter on the subject in D. Moody Smith's Festschrift. It's titled "The Historical Jesus and the Johannine Christ," which begins on page 21 of said book. Here's a snippet of what she says:
"From the way that scholars have addressed the problem of John's historicity, two observations emerge. First, 'history' and 'theology' continue to be juxtaposed as opposing categories. Despite frequent arguments that to set history and theology against each other will do violence to the character of the Gospels and especially the Fourth Gospel, such a schema continues to inform much discussion about the difference between John and the other Gospels, and John's theological agenda continues to count against its historical value. Second, it is obvious that the baseline against which John is measured is the Synoptic Gospels. While the question of literary relationship of the Gospels is not identical with, and cannot alone settle, the problem of the historicity of John, it does have implications for the historical value of the Fourth Gospel. For if the Synoptics provide reliable information about Jesus' ministry, words, and deeds, and if John differs from them at every point, can one nevertheless detect materials in John that are not only traditional but equally as useful as those in the Synoptic Gospels? The question of John's relationship to the other Gospels thus continues to play an important role in considerations of the historicity of John." (Exploring the Gospel of John: In Honor of D. Moody Smith, 26)All of that is interesting right? It gives you at least a portrait of what one person says about the issue at hand. Here's the issue folks. There is such an inclination out there to rid the Gospels of their trustworthiness and historicity that it's easy to get frustrated. People come to the biblical texts with presuppositions (myself included). This might sound like a beating drum on this website, but it has to be said again. What you think about divine inspiration means everything when we are talking about the texts of the Gospels. If no inspiration, then of course there can be all this wildness going on with data and facts and fluctuations between texts in a corpus. If inspiration, then there is some level of trustworthiness and historicity inherent to the text themselves. If something is said to have happened but it did not really happen, that is a major problem. And, in fact, it doesn't happen when we come to the texts of the Bible in general and here the Gospels in particular.
Matthew wrote his Gospel first. It was never designed to be exhaustive to Jesus' life or ministry. And John was probably involved with the composition of Matthew, as probably were the other disciples, though we almost always think Matthew wrote in some sort of isolation from those that were closest to Jesus like him. I don't know if that's the way it was or not because the text doesn't tell us. No one signed off on it like the signers of the Declaration of Independence. It would've been nice if they had, I guess, but they didn't. Getting back to the point, though, the Synoptics were written with a composition history stemming from Matthew. That's the view I hold on the origins of the Gospels. And, despite what anyone might tell you, that is a well-justified position with lots of internal and external evidence. Luke, who wrote second, did not set out to write a new Gospel or one that honed in on different elements of Jesus' life. Nevertheless, he did include new data for us. As he found it during his research, he pruned the base narrative he worked with (i.e., Matthew) and inserted additional material as space allowed and what he thought would be beneficial for predominantly Gentile believers. So, there was no need to reach back into the earliest portion of Jesus' ministry. He does help us understand the birth accounts better, and he gives us some other things that Jesus taught in the Sermon on the Mount/Plain, for example. But the narrative moves forward. The same we see really with the Gospel of Mark, which is the record of Peter's messages spoken in Rome. Still, he had the same narrative trajectory. That's why we see such similarities. He picks up with the beginning of the public ministry of Jesus, showing a transition of John to Jesus, something we also see in the Gospel of John. And he zips through the record of Jesus' ministry, focusing as they all do on the last week of Jesus' life.
What does John do, probably towards the end of his life? He probably thought to himself, "There is no way I can leave this earth and not tell people about some of the other things that Jesus did, showed us, and told us." He had an opportunity to give us a little information about Jesus' life and ministry that we didn't already have, and he took it. Well, that and the Holy Spirit probably prompted him to do it, so that all of us would have it today. That's why he reaches back. He tells us about how two of the disciples of John, one of whom (if not two) would later become one of Jesus' apostles, responded to John's testimony about Jesus being the Lamb of God. They did what was natural. A voice crying in the wilderness is announcing the coming of the king. When the king shows up, you stop following the voice and you follow the one the voice was talking about the whole time.
I think we have to just stop and reconsider the historical setting for John to write his Gospel. I think if we start here, we can arrive at the fact that the historical value for John's Gospel is quite significant, equal to the historical value of the Synoptics. After all, think about how much we would miss regarding Jesus' life if we didn't get John. The Synoptics focus about forty percent on the last week of Jesus' life. John focuses about forty percent on the last day of Jesus' life. That's pretty significant. And we should treat it as such.