I agree, spacers are almost always measured in MM, so the PO must have used wheels with a really odd offset for the XF. Spacers by themselves shouldn't be an issue with the car, assuming they are in good shape (aren't bent or cracked). The only real concern with spacers, especially if you aren't the person who installed them, is to make sure that the PO bought lugs or studs that are long enough for the wheel/spacer combo. You don't want to use stock length lugs on wheels where spacers are used as you want as much of the lug threading to make contact with the hub. This would be the only thing I would be concerned about if I was you.