Section 27. The tax due upon any estate or part thereof or upon any interest taxable under this chapter shall be deemed to be assessed at the time when the return required by section twenty-two is filed and at the amount shown as the tax due on said return or at the amount properly due under this chapter, whichever is less.

If the commissioner determines from the verification of the return, or otherwise, that the full amount of any tax due under this chapter, or any portion thereof, has not been assessed or is not deemed to be assessed, he may assess the same with interest as provided in chapter sixty-two C, at any time within one year after the date when the return and all supplementary information and documents required by the commissioner, including a copy of the final determination of federal estate tax liability in cases involving a federal estate tax return, are filed or within six months after the date of the final determination of value under sections twenty-five and twenty-six, whichever is later. He shall certify the additional amount so due and payable to the person by whom the tax is payable. Any tax so assessed shall be due and payable thirty days from the date of the certification.

Any assessment and certification may be made upon account of the tax payable upon the estate generally or upon account or in full for any part thereof or any interest therein. Payment of the amount so certified upon account shall be a discharge of the tax pro tanto and upon subsequent assessment and certification of the full amount of the tax payable upon the estate generally or upon any interest therein or part thereof, payment of the full amount of said tax shall, except as hereinafter provided, be a discharge of the tax. If upon final assessment and certification it shall appear that any payments made on account are in excess of the tax in full as so determined, the commissioner shall refund such excess without further application and without any appropriation therefor by the general court.

In determining the amount of any tax under this chapter, the commissioner shall not be required to consider any payments on account of debts or expenses of administration which have not been allowed by the probate court having jurisdiction of said estate. In lieu of allowing any itemized deductions on account of debts, expenses of administration or federal estate taxes, the commissioner shall allow a standard deduction for aggregate values subject to taxation under this chapter of less than one hundred thousand dollars, determined under a table of deductions issued by him and approved by the commissioner. Such standard deduction shall represent a reasonable amount for debts, expenses and taxes for each bracket of such aggregate property. If an executor, administrator, trustee or any person liable to taxation under this chapter, who qualifies for the standard deduction does not elect on the return required under section twenty-two to itemize deductions on account of debts, expenses of administration and federal estate taxes, the standard deduction under said table of deductions shall be used to compute and assess the tax due under this chapter.

If after assessment and certification of the full amount of the tax upon an estate or any interest therein or part thereof the estate shall receive or become entitled to property in addition to that shown in the inventory or disclosed to the commissioner at or before the time of the assessment and certification of the tax in full, the executor, administrator, trustee or other fiduciary shall forthwith notify the commissioner who shall, upon being thus or otherwise informed, assess the amount of additional tax, if any, due and payable thereon and shall certify the said amount to the person by whom such tax is payable, which amount shall be due and payable thirty days from the date of the certification; provided, that a fiduciary shall be personally liable to pay only so much of said additional tax as is computed on the additional property actually received by him and that a beneficiary receiving any part of such additional property shall be liable to pay so much of the tax thereon as is not chargeable as aforesaid to a fiduciary.

An executor, administrator, trustee, grantee, donee, survivor or beneficiary aggrieved by any determination of the commissioner, as the case may be, may, within one year after the payment of any such tax, apply by a petition in equity to the probate court having jurisdiction of the estate of the decedent for the abatement of the tax, or any part thereof. If the court adjudges that the tax, or any part thereof, was wrongly exacted it shall order an abatement of such part thereof as was assessed without authority of law. Upon a final decision ordering an abatement of any part of such a tax, the state treasurer shall pay the amount adjudged to have been illegally exacted, with interest as provided in section forty of chapter sixty-two C, without any further appropriation therefor by the general court.