Formal:
* Anthology: This is a common and formal term for a collection of stories, especially written ones.
* Corpus: This implies a large and significant collection of stories, often for academic or research purposes.
Informal:
* A cycle: This term suggests a series of stories that are connected in some way, like a saga or a mythology.
* A tapestry: This evokes a collection of stories woven together, highlighting their interconnectedness.
* A trove: This implies a collection of stories that are valuable and treasured.
* A repertoire: This suggests a collection of stories that are known and familiar to a particular group or person.
Ultimately, the best collective noun for stories will depend on the specific context and the effect you want to achieve.