With TOS , or other causes too I suppose..., you can have what is called a double or triple crush.
where the nerve is impinged or compressed at multiple places.

For instance if your EMG shows ulnar damage you could still have compressions farther up in the the BP area.
If someone also is having carpal tunnel symptoms along with the ulnar, that would be called a triple crush. BP + ulnar + carpal

With that scenario most likely you would have some other symptoms showing in your neck, shoulder, whole arm/hand, etc.??

One of the TOS members had it explained this way.

The nerve {ulnar} is about 3 feet long , any compression or impingement { even sticky tissues} could cause symptoms to "show" down the line from the c spine where it originates.

I had ulnar sx for about 2 months - but those sx were really from extremely tight /spasmed muscles in my neck and upper back.
They were pulling the vertebra and causing pressures on the nerve.
I also think the sticky fascia scenario was a big component for me.

I don't know if this might apply for you, but just wanted to give the info, TOS is often mis dx'd as something else or not dx'd at all.
Another one of those rare syndromes