[Vaduz]

Isn’t #12 the hardest?.

[Eric in the Ozarks]

I don't think there is a #12. At least I've never heard of the designation.
West KY coals are part of the Illinois Basin and is medium-high sulfur with 12,000 + BTUs.
East KY is part of the Appalachian coal producing states. The coal is harder and the various seams carry names like “Big Sandy,” Pocahontas, etc. Both are considered bituminous coals. Western coal from Wyoming is softer, lower BTU but contains very low sulfur (IE .35-.50 %) It is considered sub-bituminous. The hardest coal would likely be anthracite from certain areas in Pennsylvania. This coal is often found in "U" shaped seams, seemingly squished into this odd condition by the rise of the Appalachian chain.