Quite frankly, I doubt they even bothered with even that token effort to find excuses for failing people. They didn't need them. Everyone knew the game; if you were black under Jim Crow, you pretty much failed the moment they forced you to take it, regardless of your answers.
Literacy tests were only meant to give the threadbare illusion of objectivity to their disenfranchisement efforts and make that effort more efficient in the process. It's unlikely any state or county ever bothered to assemble a common "official" literacy test, or that officials ever put much effort into crafting a perfectly ambiguous question no one could every answer correctly. There was no need, and to the extent any did, it would likely have been just to make taking the tests as painful and humiliating as possible to punish the test-taker for not accepting that the fix was in, and to further discourage anyone else from bothering them.
Truthfully, the humiliating aspects of the various disenfranchisement mechanisms were almost certainly quite intentional. Fury over the perceived humiliation of the loss of the Civil War, and the changes wrought by Reconstruction, was the constant underlying theme of Redeemer[1] messaging. Simply regaining political power wasn't enough to slake that anger.