19 CFR 159.38: Rates for estimated duties.

For purposes of calculating estimated duties, the Center director shall use the rate or rates appearing to be applicable under the instructions in this subpart to the merchandise involved. When it is not yet known what certified rate or rates are applicable or no rate has been certified, the Center director shall take into account all the information in his possession and shall use the highest rate or combination of rates (i.e., the rate or combination of rates showing the highest amount of United States money), certified or uncertified as the case may be, which could be applicable.