Yes, the minimum thickness is usually stamped right onto the rotor somewhere. You can confirm if someone cut them to below this thickness if you've got a caliper handy. They are not supposed to cut them below that, if a dealership or shop did I would take it back in a hurry, since that is just plain dangerous. Now, is it good to cut them at all? I wouldn't, not on an 850. The production thickness of these rotors isn't very far from the minimum already, so the most you will usually be able to get is maybe one cut. But, as has already been said, the chances of the rotor warping are much higher the thinner they get. Considering how cheap OEM rotors are for this car I wouldn't even think about it, just buy new ones.

The rotors on my vintage Mustangs were so thick you could use them as boat anchors. They could take 2 or 3 cuts without even thinking twice about it.