(a) Any good conduct time credit earned by or otherwise granted to a prisoner prior to enactment of this article, under laws existing prior to the passage of this article, shall be computed by the Department of Corrections through the date next preceding May 19, 1980 under such laws and such time credit, less any forfeited, shall be granted to the prisoner.
(b) The provisions of this article shall not be applicable to any prisoner serving time prior to May 19, 1980, nor to any person who commits an offense prior to May 19, 1980, even if such person is sentenced after May 19, 1980. Deductions from the sentences of such persons shall be earned at the same rate as provided by law prior to May 19, 1980. All constitutional rights, remedies and privileges of such persons shall not be reduced, diminished or abolished.