Let's break down the statements:

A. Contents of the text can be classified into narrative and didactic. - True. Mahabharata comprises both narrative sections (like stories) and didactic sections (containing teachings or moral lessons).

B. The narrative section contains stories. - True. As mentioned earlier, the narrative part includes various stories and episodes.

C. The didactic section contains social norms. - True. Didactic sections often convey social norms, ethical teachings, and codes of conduct.

D. The narrative section was added later. - False. There isn't concrete evidence to suggest that the narrative sections were added at a later stage. Both narrative and didactic elements are integral parts of the Mahabharata.

E. The text 'Mahabharata' is described as an 'itihasa' within early Sanskrit tradition. - True. 'Itihasa' is a term used in early Sanskrit tradition to describe epics like the Mahabharata and the Ramayana.

So,the correct option is [4].