As for the problem of always having another answer give a positive sound - is that just for the first step of an adventure? It very well be the answer to the first step in one of the other adventures or even an upcoming expansion?
I'm not sure how the decoder is working, and I didn't run tests on it, but since we're not telling it what mission we're doing, all of the first steps should show as valid when you start. If the rest of the steps aren't always valid, they should become valid after we tell it which mission we're doing with step one.
Not sure. It was the first step of the adventure so guessing we just lucked into a random working code. Almost a shame you don't have to tell it what scenario you are doing to avoid this, but I realize it would complicate things.