This act shall become effective on the first day of the second calendar month after the month in which it is finally enacted; and all taxable sales during that month and for a period of two years thereafter shall be subject to tax hereunder. The expiration of the period during which tax is imposed by this act shall not relieve any person from the filing of returns or from any taxes, penalties or interest, imposed by the provisions of this act, or affect or terminate any petitions, investigations, prosecutions legal or otherwise, or other proceedings pending under the provisions of this act, or prevent the commencement or further prosecution of any proceedings by the proper authorities of the Commonwealth for violations of such act, or for the assessment, collection or recovery of taxes, penalties or interest due or owing to the Commonwealth under this act.