Ah yea, sorry, I mean in addition to what we already know for sure—Timbuktu is emphatically not what I was referring to (although—I had forgotten about Timbuktu libraries, and it makes my point better than I did, so I appreciate your bringing it up!). I'm referring to oral evidence of writing in Great Zimbabwe (among other places I'm sure). If they had developed script, we unfortunately lack evidence of it.

My point more broadly is that prevalence of an oral tradition doesn't imply the lack of capacity to develop a written one. As Timbuktu is perfect evidence of—their libraries coexisted (and still do today) with griots, and the two repositories of knowledge seem to serve distinct functions in society.