I don't think I put much stock in this work, but I have wondered how far back some on those stories might go. Maybe way, way back?
many of the fables began as oral stories that left no written versions
I would say that ALL the stories were initially verbal only. There was normally a 'story teller' in each group whose responsibility was to commit stories and tribe history to memory and for a suitable payment (libation?) 'play them back' to the assembled tribe. This is still the case today in many areas less well served by Elon Musk.
"How did we record history before we understood writing? In most cultures, the only way we remembered the past was through passing on stories word-of-mouth from one generation to another. These stories teach us lessons, give us history, and help us remember where our traditions come from, and in Lakota culture, we hold that you must tell every story just as heard or it loses its meaning."