You can't research every supplier at once. List yours with their share of spend and what you know about each, and see where your FEOC exposure sits and which three to check first.
A ranking on your answers: share of spend times how little is known, with any warning sign counted as knowing nothing. Not legal or tax advice.
Under the material assistance rules, a product counts against your cost ratio if it was made by a prohibited foreign entity, so a large supplier you know little about can move the ratio more than several small ones. And a supplier's word only goes so far: a buyer may not rely on a certification it has reason to doubt. Start where the most spend meets the least evidence.
Next: see what your unknowns do to the ratio with the cost ratio calculator, or go through a supplier's paperwork with the certification checker.