Michigan Compiled Laws, Chapters 760 to 777 Code of Criminal Procedure § 769.14

Sec. 14. Any person now incarcerated in any state prison, or on parole from a sentence thereto, who was sentenced under the terms of sections 10, 11, 12 or 13 of this chapter  1 as in effect prior to the effective date of Act No. 56 of the Public Acts of 1949, shall be entitled to a review of sentence upon application to the court in which he was sentenced. Upon such application any judge of such court may vacate the previous sentence and impose any lesser sentence which in his judgment might have been imposed under sections 10, 11, 12 or 13 of this chapter, as amended by Act No. 56 of the Public Acts of 1949, had such sections as amended been in force at the date of the previous sentence imposed upon said prisoner: Provided, That any sentence so imposed shall be deemed to have begun as of the date of the previous sentence, and the rights of such prisoner under the laws shall be governed by the lesser sentence as then imposed.