Right now, people convicted of sex offenses BEFORE 1995 don't have to register, thanks to a ruling by the Missouri Supremes. But legislators are working to change the state's constitution and make it mandatory. From The AP:
Senators gave initial approval to a proposed constitutional change that would carve out an exemption for the registry law. The change would also retrospectively apply a prohibition on sex offenders living near schools and a requirement of felons to submit DNA samples.