Our legal system in the United States is always changing and evolving in an attempt to have the most just and fair system. In some cases, when changes are made, those affected by old policies have a chance to be resentenced with newer policies in mind. One great example of a time where we saw the evolution of a legal system is in the situation of California.
The California three strikes law was changed in 2012 so that people who were being sentenced for a third charge had to have committed a serious or violent felony in order for the three strikes law to apply. This was good news for many people who were convicted and sent to jail for 25 years to life because of their third nonviolent felony. These people can now be resentenced and in some cases set free.