If any private car company refuses or fails to make and return the reports required by section 137.975 within the time prescribed and without an extension of time, the commission shall increase by four percent the total assessed valuation of the distributable property of any such company, unless the commission, for good cause shown, waives such penalty. Any such reports, or any payment of taxes required by section 137.022 and sections 137.975 to 137.985, delivered by United States mail to the proper official shall be deemed to be received as of the postmark date stamped on the envelope or other cover in which the report is mailed. In the event any report is sent by registered or certified mail, the date of registration or certification shall be deemed the postmark date. Reports required by section 137.975 may be furnished to the commission by an express or overnight carrier, and such reports shall be deemed to be received as of the date after the reports were sent by way of such express or overnight carrier.