How do we know that not a single one of the accused was a witch?

I haven't seen any proof in those history books. The historians are just assuming that, because we've been mislead to believe that witches aren't real. Speculation is not proof.

What evidence do I have? They put them on trial and found them guilty. Now, I admit trial by judge or jury isn't as fair as trial by ordeal because you are leaving it up to humans instead of God, but still most of the time the jury arrives at the right verdict. It's only rarely that someone is falsely convicted, and if those people lead virtuous lives oh well they went to heaven anyways.

1 or 2 may have been innocent, but they would've been spared if they had used trial by ordeal instead. Not necessarily the drowning test, but maybe having them scalded and seeing how fast the boils heal. When people are accused and you have a trial by ordeal to see if they are innocent or guilty so long as those people believe in God and are innocent then God will cause the boils to heal by the deadline for the verdict.