David makes a good point here. Like if a person is released because of overcrowding, a liberal judge, a soft parole board etc. Should 15 months of a three year sentence be considered a complete sentence? Case in point, the Memphis random shooter a couple weeks ago.In a perfect world, that would make sense, but in our society, the convicted seldom serve the full term before being released, for many reasons.
But then again, in a perfect world, everyone would have excellent self control so there would be no need for any laws.