Upon written request from an assessing unit, and upon good cause shown, ORPTS may allow an additional period of time from the expiration of the time period provided in section 8186-15.2(a) of this Subpart. Such written request must be received by ORPTS prior to the deadline for submission of the complaint form and supporting documentation. For purposes of this subdivision, good cause shown shall include extraordinary unforeseen and unavoidable circumstances that have arisen subsequent to the establishment of the tentative rate or ratios.