For this reason alone I love Post apocalyptic scenarios. Whatever context that I Roleplay in I attempt to immerse my character in whatever current situation they are facing. Obviously with the huge loss of recorded knowledge a tribal could never truly RP as if they knew everything pertaining to the past. I was hoping to use the current lore to explain in part how tribal of this current era could have some prophetic dreams regarding Elder Gods/Gods of old. I also enjoy your idea regarding the books....textual evidence could also be an interesting thing to play with.