My experience is that U.S. government people rely very heavily on the information provided by expert panels. They also engage experts in their own bureaucracy to try to double-check or extend that analysis.
Often, the policies of the U.S. of late have been that when new perpetrators or sanctions violators have been found by expert panels, we lobby heavily within the Security Council to get those people listed and sanctioned. When that's not possible, OFAC does its individual foreign policy work and uses the existing—even thin—UN sanctions that are in place as a springboard for the U.S. system to then impose targeted financial sanctions and the like.
This, of course, has led to a small set of disagreements with the Russians and Chinese, who believe that sanctions set by the Security Council are the global norm and the ceiling that you can't go beyond, but I think the U.S. and many other western states believe that when you have that global agreement, the nations doing individual implementation can use it as a springboard rather than being constrained by a ceiling.