If it could help...

I do a curve.
Then I revolve it with or without cap. With cap I delete it to test.
When I do my shell, the "in" surface and "out" surface is one and only 1 surface.
I can't separate them.
So it's "normal" you could not cut and find distinct edges.

If the shell is done "fliped" we don't have this problem.

If the shell is done with centerline, we can't have something done.