A bunch of them are for infant minor injury where it's like don't do an X-ray. If you can see a break on the image you'd do A, but if you can't you'd figure the break might be too small to show up and do A anyway. Kids don't need more radiation, just do A immediately without requesting an X-ray.
I have wondered if my cancer diagnosis is at the edge of this case. There's a step where they do a needle biopsy. But, as far as I can tell that biopsy always either says "Cancer" or "Don't know" and I'm not sure what else they'd do for "Not sure" beyond the next step in the cancer diagnosis...