The Talmud tells us that the Sages had long discussions about which books should be included in the Tanach [Bava Batra 14b-15a]. Their decisions were important. First, the books they excluded do not have to be studied. Second, they do not have to be included in yeshiva libraries, which caused many to have disappeared completely. Third, and most importantly, they cannot be used to expound on the meaning of Torah verses.
But I don't know of a similar process for acceptance of midrashim. Was there one? Where? Is there a list of "accepted" midrashim for the three purposes listed above? Where?