You can read the whole series here.
Passion narratives in the Gospels differ from the rest of the respective content in several ways, this is one. The Passion stories of Mark, Matthew, Luke, John have a sort of built in consecutive character. And that probably represents the second epoch. It’s just natural. You must have a conspiracy, a capture/arrest, a trial, a conviction, a death. The ordering is just there, though there are some variations. Some people have argued that no such ordered narratives existed until Mark, the earliest Gospel. This seems odd and I don’t think it can possibly be true. This contrasts with the rest of the Gospel stories in several ways. There is no implied sequence for most of the them. For example, the parable of sower and seed. One Gospel has it in one place, another Gospel puts it in a different place. There isn’t anything that clues you in to where or when it was said. Jesus heals the blind man. Where was he? It doesn’t say. Sometimes there is a place name attached to an event, but one Gospel puts it when he comes into town, another puts it when he leaves town. The sequence of events is not part of the story, and it’s obvious that there are different (oral and perhaps written) traditions in play, and that the Evangelists themselves exercise freedom over the placement of traditional events.
The Passion is, as I said, different. You can’t have an execution without a trial and sentence. For that to happen, there had to be an arrest, etc. Paul hints that this kind of consecutive Passion story was available early on. In 1st Corinthians he says he got it in the tradition that Jesus was crucified, was buried, and then rose. Probably he’s talking material from the thirties, he’s writing in the fifties. And he says, that “on the night Jesus was betrayed, he took bread . . .” the basic features are being transmitted in the tradition. The sacrament (Eucharist) was instituted on the night of the betrayal/arrest (in the Synoptics). All this is well before Mark. Mark gave contours to such tradition, supplied a shape for the traditions he encountered. But he didn’t invent the Passion sequence.
The Passion stories are like the ones surrounding Jesus’ birth, they are genuine narratives, rather than vignettes like the rest of the Gospel(s).
One more point about the Passion stories: they are not even primarily focused on Jesus, at least in Mark and Matthew. More than half of the text circles around others, particularly Peter. There are several parallel dramas happening. For example, what Jesus does in Gethsemane is about a third of the scene. The rest is about the disciples. John is interested in Pilate. Half of that trial scene is all about Pilate, not Jesus. The intent may be to get the listener (reader) to be an identified participant. How would you react?
Next: a sub-series on Gethsemane.
 What happened is what we experience every day with story arcs. You hear a story, maybe a bit of gossip or something. It circulates and you hear it from someone else later on. Some features or names may have changed, been added, been left out. If it gets written down by different people, or at different times, you get different versions. They have things in common, but there are differences. One might preserve certain things, another one preserves different elements. An example from the Passion, “My soul is sorrowful even unto death” (Mk. 14:34, Mt. 26:38) it’s a quote from a Psalm (Psalms 42:5-6). John has “Now is my soul troubled” in an earlier spot. They are two parts of the same Psalm verses. This suggests that the tradition(s) involved this verse very early on, but that there was a division, a crossing, at some point. The First Vision is a great example. The canonical version is crisis literature. The tradition needs a more robust anchor, and that’s a part of the internal explanation for that version.