Any assessment not paid when due shall be increased 1.5 percent each month beginning with the day following the date such assessment was due. Any remaining amount due, which shall include any unpaid charges previously made pursuant to this section, shall be increased at the same rate on the corresponding day of each month thereafter until paid. For the purpose of this section, any assessment that was determined at a date later than prescribed by this subpart because of a person's failure to submit a report to the Board when due shall be considered to have been payable by the date it would have been due if the report had been filed when due. The timeliness of a payment to the Board shall be based on the applicable postmark date or the date actually received by the Board, whichever is earlier.