Is a manufacturer that uses the term “naturally gluten-free” in a food that is generally considered “naturally gluten-free” responsible for verifying that the product meets the FDA definition of < 20 ppm?

Yes, the manufacturer must ensure that any potential cross-contact results in a product with less than 20 ppm of gluten. For GFCO certified products, the threshold is stricter and should contain no more than 10 ppm of gluten.