Difficult to answer. How many times should a convicted person be able to bring forward new evidence to correct a false judgement? After years new evidence based upon new forensic science can change a judgement fundamentally. In cowboy countries they give a damn about truth, fight is all and god is the only judge. In more civilised countries we reevaluate and evaluate evidence and try our best to come as close to the truth as human effort can bring us. But, big but, grinding a soul many times through the mill stones of justice can be a crime too. I do not know where to draw the line between too many and too less. Human efforts are so limited and in vain too often. But keep yourself away from simple desires of revenge and hate. It darkens your own soul in the end.