Source: H. Graetz, History of the Jews, volume II (Philadelphia: Jewish Publication Society of America, 1893) 460-461.
"The style of Judah's Mishna is concise, well-rounded, and intelligent, and is thereby well adapted to impress itself firmly on the memory. He in no way intended his Mishna, however, to be regarded as the sole standard, having in fact only composed it, like his predecessors and contemporaries, for his own use, in order to possess a text-book for his lectures. But by reason of his great authority with his disciples and contemporaries his compilation gradually obtained exclusive authority, and finally superseded all previous collections, which for that reason have fallen into oblivion...His disciples disseminated it through distant lands, and as a religious and judicial code."
At some point in the future, I want to redo some reading on the Mishnah. In my class a while back, I learned that there are different ideas about what the Mishnah actually was. Was it a text-book? Or a judicial code? I never heard that it was Rabbi Judah's lecture notes, but who knows? It may have been that, at least partially. I vaguely recall reading that parts of the Mishnah came after Rabbi Judah, but I don't remember what the rationale was for that claim.