When Adam and Eve sinned in the garden of Eden, their eyes were opened and they knew what was good and evil. This does not mean that they acquired new knowledge in addition to what they knew before.
The “knowing” what is good and evil signifies a complete reversal of man’s knowledge. Up until that moment, all Adam and Eve knew was God and everything good. Yes the devil had already fallen at that time and he may have been creeping around finding a way to destroy God’s creation. But until Adam and Eve gave in to the temptation, their focus was solely on God and His presence.
After the fall, their first realization was their nakedness. They knew right away that something was missing.
When Adam and Eve fell to temptation, they lost sight of what is, and started being conscious of what isn’t there. No, they didn’t acquire new knowledge. They shifted their focus. From God. To something else.
Inspired by Dietrich Bonhoeffer’s Ethics (Touchstone, 1955).