While most Amoraim were familiar with the mishnayot of the sedarim which formed the curriculum of Amoraim study, such familiarity was not universal. … Even when a relevant mishnah is cited, it is not always verbatim. …
The difference between the Bavli’s citation of mishnayot and those of Toseftan baraitot is that the text of the Mishnah has been transmitted along with that of the Bavli from the earliest times.
Yaakov Elman, Authority and Tradition: Toseftan Baraitot in Talmudic Babylonian (New York: The Michael Scharf Publication Trust of the Yeshiva University Press; Hoboken, NJ: Ktav Publishing House, 1994), 48.
In a statement repeated several times in Shas, Rava emphasizes the importance of an individual’s input in Torah study, that is, the process of making Torah one’s own. Let us look at AZ 19a, where this appears in the context of Rava’s ‘musar shmuess’ regarding Talmud Torah. … In other words, our task in studying Torah, if we merit it, is to put our own individual stamp on Hashem’s Torah by filtering it through our own understanding, as limited as that may be. The souls of Kelal Yisrael were all at Mattan Torah, and we each have our own portion of Torah assigned to us. Of course, that understanding, even if part of our ‘self’ contributes to it, must reflect true Torah values and modes of thought and argument. Clearly, this individual stamp on Torah learning applies to the Amoraim; after all, Rava was first and foremost addressing his own colleagues, who were Amoraim. Thus, we should expect that each Amora has his own individual understanding of various issues, and when they differ, seemingly isolated differences might be understood as expressions of a more general outlook.
Yaakov Elman, “Rava as Mara de-Atra in Mahoza”, Hakirah 11 (Spring 2011), 61-62
…an appreciation of the role played by the stam in the sugya, which is distinguishable from that typically played by amoraim. The stam often takes upon itself tasks that affect the sugya or sugyot as a whole…. The tasks of the amoraim, in contrast, are localized, consisting of the interpretation of a particular tradition, stating the law, resolving or posing an objection, or answering or raising a question. … It is the way of the stam to offer artificial responses, sometimes to teach us why a particular argument was chosen over another, sometimes to increase the complexity of the argument, and sometimes to weave together independent traditions or discussions.
Richard Kalmin, “The Function and Dating of the Stam and the Writing of History”, in Melekhet Mahshevet: Studies in the Redaction and Development of Talmudic Literature, ed. Aaron Amit and Aharon Shemesh (Ramat-Gan, Israel: Bar-Ilan University Press, 2011), 40-41 (English section).