Interesting, I see both sides. I agree completely with you that they shouldn't extrapolate. But in the case of attempted murder, wouldn't this just mean proving beyond doubt that someone tried to kill? If there is doubt that the accused meant only to harm, for example, then I get it. But if they provably tried to kill, however you prove that, then I see the argument that it's irrelevant whether they succeeded or not.

Anyway, it's moot imo because I don't believe in a retributive justice system, I think the only concern should be preventing recidivism. But your post has made me think a bit, I'm still not sure what the "right" answer is here