As of December 1, 2015, Michigan law was amended to require that the training for a CPL application be provided within 5 years preceding the date of application.
Prior to this amendment, there was no such requirement. Every county clerk handled the issue differently. Some required the certificate to be within 6 months, some never considered it expired.
See Public Act 372 of 1927 Section 28.425j for the complete law with references.