The average sentence imposed on the 9,700 sex offenders was 8 years and, on average, 3 1/2 years of those 8 years were actually served prior to release. The average sentence imposed on the 4,300 child molesters was approximately 7 years and, on average, child molesters were released after serving 3 of the 7 years.
https://www.bjs.gov/content/pub/press/rsorp94pr.cfm
Parole or probation is only imposed on people who have not fully served out their time and is released early With the average of 4 to 4.5 years of early release, government supervision is only required for those years that remain on their sentence. Registration of a sex offender is not necessarily considered part of the parole or probation as, individuals who are released following serving their full term in prison is still required to register. They can be arrested for not following the registration requirement but they are no longer on parole and therefore cannot be sent back to jail for a parole violation.