§ 33-a. The provisions of sections five, twenty-two, twenty-six,
forty-seven-a and forty-nine-a of this act in respect to the mailing and
publishing of notices are for the benefit of taxpayers and shall be
construed to be directory only and not mandatory and the failure to mail
or publish such notice or failure of the addressee to receive the same
shall not invalidate or affect the validity of the taxes on or the
penalties imposed by law upon, or of any tax sale of, real property
affected thereby.