It is rare
In most people, the tip of the spinal cord is at the bottom of l1, the first bone in the lumbar spine, so all lumbar disk herniations miss the spinal cord, even large ones.
There are some folks with tethered cords, so the spinal cord is elongated. Since the tether can cause the cord problems, in such cases a large disk herniation could be double jeopardy. This is rare but serious.