...we don't know, but let's try and agree on a time span.... OK?
Most historians place G-Mark as the first to be written, circa 50-70 CE. Let's say 60 CE...? Which means that It was written just after the lifetimes of most of the witnesses.
Well, you know, that's for your own individual investigation.
Cultures that are mostly illiterate become better at oral tradition. For oral tradition to reach across a few decades is a doddle. Some societies have passed down their history over many many generations, I believe. So the only folks who could answer your question to an academic standard would be the anthropologists, is my guess.
I am not proposing certainty, you understand, just plausibility <-> probability.
Is G-Mark a different version of the Mark that's in the Bible? If not, do you have a link?
Anyway, the miracles in Mark would be right out of the window, too. If it came from an oral tradition, it makes sense that they would be embellishing it more and more as time went on.