At the time of the trial the information was deemed to be correct. Therefore the punishment was justified at the time of the trial. The fact that the information later turned out to be incorrect is a moot point.

If someone is charged with murder and the evidence at the time of the trial says that they did, in fact, commit murder and they are punished for it, the punishment is deserved at the time. If evidence later clears the person that doesn't make the initial punishment any less justified.

Judges can only make decisions on the evidence they have presented.