Anunna, or Anunnaki in its Akkadian form, is not a name but a collective. In Sumerian it is written a-nun-na, usually understood as the offspring or the seed of An, the sky god, and in the earliest usage it means simply the great gods taken together: the assembly that meets, deliberates and fixes destinies. When a Sumerian text wants to say that a decision was final, it says the Anunna made it.
The term is often paired with a second one, the Igigi, and that pairing is where most of the confusion begins. In the Old Babylonian poem Atrahasis the Igigi are the junior gods who dig the canals and carry the baskets, who throw down their tools in protest at the work, and whose strike is settled by the making of human beings to do it instead; the Anunnaki are the senior gods for whom the work is done. In the Enuma Elish, Marduk divides the Anunnaki after his victory, assigning three hundred to the heavens and three hundred to the earth, and they build Babylon for him in return.
By the later Akkadian period the sense has narrowed, and in places inverted. The Anunnaki become gods of the underworld, and the Igigi the gods of heaven. That is the sense governing the descent of Inanna, where the goddess is brought before the seven Anunna, the judges of the great below, who fix her with the eye of death. A reader meeting the word in two texts a thousand years apart is not meeting a contradiction so much as a term that moved with the theology around it.