Section 31. If the assessment of any tax is in excess of the amount shown on the return as the tax due, the commissioner shall, as soon as may be, give written notice to the taxpayer of the amount of the assessment, the amount of any balance due and the time when the same is required to be paid. Failure to receive such notice shall not affect the validity of the tax. In the case of 1 or more corporations that participated in or are required to participate in a filing through the means of a combined report under section 32B of chapter 63, the commissioner may issue a single notice directed to the principal reporting corporation on its own behalf and as the agent for each corporation that is being assessed. This single notice shall state the net cumulative liability of all such assessed corporations.