Differences in flywheels through the years?
 

I've got 4 flywheels laying around, 3 different styles/kinds/part #'s. Does anyone know what changed over the years and why? I have 2 that I think are early firstgen flywheels that are thinner overall but the mounting surface that goes to the crank is raised. There is a raised ring around the outside circumfrence of the face. I have one I think is from a 93 that is thicker, has a flat back and that same ring on the outside face. I have another one that is thick like the last one except it doesn't have the raised ring on the face, its flat. When laying side by side all the ring gears and faces line up w/ each other. Any ideas?