Good question!
Here's a blurb from the Michigan government instructions that should address it:
"SSA exempt employment is not covered by the federal SSA, which means the worker did not pay Social Security taxes and is not eligible for Social Security benefits based on that employment. Almost all employment is covered by the federal SSA. The most common instances of retirement and pension benefits from employment that is not covered by Social Security are police and firefighter retirees, some federal retirees covered under the Civil Service Retirement System and hired prior to 1984, and a small number of other state and local government retirees. Federal retirees hired since 1984 and those covered by the Federal Employees’ Retirement System are covered under the SSA."
