I've been rereading Michael Wood's 'In search of the Trojan War' as a back grounder for planning a visit to the Mani later this year, and sad anorak that I am I was going to sneak some visits to Mycenean and Byzantine sites into the holiday plans. (Vigorous walks and scrambles to some of the smaller sites)
However, rereading the book, what I was struck by was the idea that literacy developed as a result of the need to count and record things, and that if you do that you can plan - so in essence we have complex societies which we can distinguish by their need and ability to plan - which in turns requires information, how much land, how much grain, how much does a soldier eat etc.
Even these great literacy standouts, the Inca used khipiu to count things in complex ways.
So we can say that literacy developed as a way of making and recording lists of things, as a set of aide memoires, and we can then probably guess that full literacy started as something like a set of flash cards to aid the remembrance of oral poetry for the purposes of recitation.
What of course would be even more fascinating if we did find one of these flash cards, though how we could tell from a list might be a tricky question:
For example is
20 slave girls
5 swords lost
an account, a situation report on a battle lost, or a performer's flash card?