Mich. Comp. Laws § 38.1076

Sec. 76. A qualified participant who was a member, deferred vested member, or former nonvested member of Tier 1 who makes an election to participate in Tier 2 pursuant to section 61, shall be credited with the years of service accrued under Tier 1 on the effective date of participation in Tier 2 for the purpose of meeting the vesting requirements for benefits under section 75.