Really started adding. This is the key quote:

    Second, we document that, following the enactment of the federal law,
    some food manufacturers engaged in risk mitigation by adding small
    amounts of sesame to products that previously did not contain the
    ingredient. Doing so allowed firms to use the safe harbor provided by
    the allergen labeling rule rather than the ambiguous and non-protective
    “may contain” precautionary labeling. This was most observed in the breads
    and buns category, products for which the prevention of cross-contamination
    may have been more challenging and the likelihood of a recall or litigation
    higher.