Mass. Gen. Laws ch. 65 § 25
The value of property upon which a tax under this chapter is due shall be determined by the commissioner within six months from the date when the return provided for in section twenty-two is filed with him. All information required by the commissioner shall be provided by the fiduciary in such form as the commissioner may require, and all copies of probate documents as may be required by the commissioner under this chapter and chapters sixty-five A to sixty-five C, inclusive, shall bear the teste of a register of probate or in lieu thereof, an affirmation, under penalties of perjury, by the fiduciary or his attorney that such document is a true copy of an original document on file with the registry of probate or allowed by the probate court in which the estate is being administered. If the commissioner fails to determine the value of the property within the prescribed time, the value of the property as submitted shall become final and binding upon him except for fraud or active concealment of essential information on the part of the fiduciary or the person liable for the payment of the tax. There may be excluded from any determination of value any property on which information satisfactory to the commissioner has not been furnished to him, or any property in which the decedent had an interest vesting in possession or enjoyment at a future time, and with respect to such excluded property or any part thereof valuation shall be made by the commissioner when satisfactory information is furnished or otherwise becomes available to him. Notice of any determination of value by the commissioner under this section shall be sent by him by registered mail to the persons by whom the tax is payable, and such determination shall be final as to all property valued therein unless the value so determined shall be reduced or altered as provided in this section and in section twenty-six.
Mass. Gen. Laws ch. 65, § 25