Section 27. If, before the expiration of the time prescribed under section twenty-six for the assessment of any tax, the commissioner and the taxpayer consent in writing to extend the time for the assessment of the tax, the commissioner or his duly authorized representative may examine the books, papers, records, and other data of the taxpayer, may give any notice required by section twenty-six and may assess the tax at any time prior to the expiration of the extended time. The period so extended by the commissioner and the taxpayer may be further extended by subsequent agreements in writing made before the expiration of the time last extended. If, as a result of such examination, the commissioner determines that the taxpayer has overpaid any tax, he shall reduce the assessment accordingly and refund the overpayment in accordance with the provisions of section thirty-six.

In the case of 1 or more corporations that participated in or was required to participate in a filing through the means of a combined report under section 32B of chapter 63, the commissioner and the principal reporting corporation may consent in writing to extending the time for assessment of any component of the corporate excise reported or required to be reported under said chapter 63 by any such corporation, whether relating to the income measure, non-income measure or a minimum excise tax liability under the corporate excise. This consent shall be effective for: (i) any corporation that filed through the means of the combined report, including any corporation that was improperly included in the combined group as determined pursuant to said section 32B of said chapter 63 or that subsequently ceased to be a member of such group; and (ii) any corporation that was improperly excluded from the combined group and that improperly filed a separate return to report its corporate excise under said chapter 63. The period so extended by the commissioner and the principal reporting corporation may be further extended by subsequent agreements in writing made before the expiration of the time as previously extended. The commissioner or a duly authorized representative may examine the books, papers, records and other data of any corporation that participated in or was required to participate in the filing of the combined report. Nothing in this section shall preclude the commissioner from separately executing consents to extend the time for assessment with an individual corporation subject to tax under said chapter 63 for a tax due from such corporation under this chapter or said chapter 63, even where the corporation participated in or was required to participate in the filing of a combined report.