Most of the traditions which were eventually integrated into the Talmud and Midrash will have originally circulated orally, sometimes for hundreds of years. The long process of transmission makes it impossible to reconstruct “original” versions of traditions, if they ever existed. Stories about rabbis and teachings associated with them will have circulated in various different versions and were adapted to the contexts and purposes for which they were retold and rewritten. Therefore, even if one assumes that a certain text had a prehistory, one cannot trace that prehistory back to its origins or early stages.
Catherine Hezser, “Form-Criticism of Rabbinic Literature”, in The New Testament and Rabbinic Literature, eds. Reimund Bieringer, Florentino García Martinez, Dider Pollefeyt and Peter J. Tomson (Leiden & Boston: Brill, 2010), 100.