When did they require an Studor-Vent be required in Michigan homes.
Myain reason for asking this what purpose dpes it serve do you have an answer for this?

A Studor vent is a brand name of a line vent. If a drain line is completely filled with water, the water flowing down the pipe will siphon the trap dry unless there is a vent pipe to let air in behind the draining water. When the trap is siphoned dry you get sewer gasses out the drain pipe. Normally this vent pipe goes through the roof.

A line vent is a mechanical vent that allows air into a drain line.
Sometimes it is not possible or not practical to vent the drain line through the roof. Where permitted a line vent may be installed. Not all plumbing codes permit line vents.

Not sure they are "required", venting is required. They may be allowed as an alternative to full venting.