As far as 2) scribes were expensive then, and paper/skins even more so. The stories weren’t written down until it was clear they were ‘hot’ and worth it.

Same with Buddhism, near as anyone can tell. None of the scripture is contemporary with Buddha.

I can even imagine one story being about "my teacher once met this dude who said we should be nice to each-other" and "a cousin heard about this guy who said that poor people should be helped by neighbors" and those somehow merged and became one person one story.

It happens today, in an era where information is/appears much more precise, people and attribution is common. e.g. quotes being attributed to Einstein or some rock-star, or actors "cancelled" for stuff some other person did or said.