Mich. Comp. Laws § 38.1646
All proceedings pending and all rights and liabilities existing, acquired, or incurred under former Act No. 251 of the Public Acts of 1935 at the time this act takes effect are saved. Those proceedings shall be consummated pursuant to the law in effect when the proceedings were commenced. Those rights and liabilities shall be preserved pursuant to the law in effect on the day immediately preceding the effective date of this act. To the extent that either the kinds of benefits available under former Act No. 251 of the Public Acts of 1935 are in effect on the day immediately preceding the effective date of this act or the manner of calculating those benefits under former Act No. 251 of the Public Acts of 1935 results in a greater benefit of any kind than would otherwise be available under this act or includes a benefit not otherwise available under this act, the determinations of those kinds of benefits available and the manner of calculating those benefits shall be made pursuant to former Act No. 251 of the Public Acts of 1935 for those members who participated in the retirement system as set forth in former Act No. 251 of the Public Acts of 1935 before the effective date of this act.
MCL 38.1646