Presumably Rebbe used his students to help in writing, same as Chafetz Chaim for Mishna Berurah. As a reference. Rabban Gamliel had 1000 people learning Torah ands 1000 Science in his household.
References to forgetting or being unsure is a good hint what was unwritten. In a recent daf, R Akiva knew of a machlokes between b’Hillel and b’Shammai but was not sure who is which side. edited