So Mark overall is shorter than Matthew – this is evidence for Markan priority.

Matthew has a pericope far shorter then Mark’s – this is also evidence for Markan priority?

The progression of the story is actually this. First Matthew’s two demon possessed man – than one man in Luke but he has many demons enter him – then the many speaking as one in Mark “my name is legion for we are many”

As a good rule of thumb the more memorable the story the later version it is – eg the paralyzed man lowered through the roof (not original, but a later edition in Luke/Mark).

Anyway in Mark’s later version of the demon-possessed-man he tells us the man was found “dressed and in his right mind” Mark 5:15

The problem with this is that Mark had never told us the man was naked. Mark 5:3 “This man lived in the tombs, and no one could bind him anymore, not even with a chain”

So where did he get the idea from that he was naked? The answer is that he was reading Luke’s version.

Luke 8:27 “there met him a man from the city who had demons; for a long time he had worn no clothes, and he lived not in a house”

It does raise an issue. Just what was Matthew and Luke’s attitude towards Mark? What do the uses to which they put Mark’s text tell us about their intent? They clearly valued Mark since they copied reams of text from him. It would be hard to claim they thought they were simply replacing him. Updating? Correcting? Interpreting? All of the above?

Yes, exactly! (I think this is a facet of the first question I asked here, concerning the intention of the gospel authors.)

It looks an awful lot like fan-fic: They are generally free with their sources: they have no qualms slavishly copying reams of material, but they also have no problem with reworking it freely and substantially.

If they thought they were correcting him (and they thought the historical facts mattered), then they would have needed some basis for correcting their own source (even if the basis was something as thin as their own theological convictions about what the messiah must have been like).

I continue to be perplexed by this.

All I can offer by way of a solution now is, first, to look at them a part of the larger scripture-writing-from-whole-cloth phenomenon of the intertestamental and early Christian world. We have lots of examples of people attempting to expand the canon from their own imagination, but basing their new works on an established canonical world. What the canonical gospel authors did wasn’t that different from what other people were doing.

Second, I suspect that they lived in a world where historical facts were to some degree disvalued because they were known to be unreliable and unverifiable. So they were essentially some sort of historical skeptics and maybe the flip side of that is that history can be whatever you want it to be: what does it matter and who is going to say otherwise? Think of our attitude today to local lore–“people say that . . .” Everyone knows it’s just hearsay, but also you can find yourself believing it just because it’s such a good story; but people also tend to embellish it to make it a better story.

Another good example, a bit closer to home, might be something like Secret Mark. I think everyone realizes that we just don’t know whether it is authentic, and yet, one can find oneself thinking on the assumption it is true, just because we want it to be true.

“Mark overall is shorter than Matthew – this is evidence for Markan priority”
Tatian’s Diatesseron is shorter than the books of Matthew Mark Luke and John combined.
Does that being-shorter mean that the Diatesseron was written before the separate Gospels were written?

“Luke 8:27 ‘there met him a man from the city who had demons; for a long time he had worn no clothes, and he lived not in a house'”
The New Testament was originally in Aramaic, not Greek. The Greek mistranslates to come up with “city” when actually what’s referred to is the open country adjoining a city or town. See Charles Cutler Torrey’s _Our Translated Gospels_ (1936) 82, 89.