Ask what a record was created to do. Distinguish a writing material, a script, and a language. One surviving record reveals a particular activity, not everything about a society.
Worked example
An account listing grain can help study distribution. It cannot by itself show that everyone in the community could read.
Writing in Ancient Mesopotamia
In southern Mesopotamia, early writing developed alongside growing settlements and economic record keeping. Later cuneiform used wedge-shaped impressions, commonly on clay. Scribes used it for accounts, letters, literature, and other purposes. Different languages could be written in cuneiform; script and language are not the same.