Whenever any board of school directors shall have heretofore sold any unused and unnecessary lands and buildings by public auction, the sale of which by public auction is authorized under the provisions of the school laws of the Commonwealth, and such board of school directors has received the purchase price, then such sales shall be valid and binding on the school district, and all deeds or conveyances given by the school district for any such lands and buildings are hereby ratified, confirmed and validated, and such purchasers and their respective heirs, successors and assigns shall hold and may convey such titles and estates indefeasibly as to any rights of the school districts therein, notwithstanding the fact that the notice of the public auction was not published in the legal newspaper in the county or by posting of handbills nor in one or more newspapers of general circulation published within the county or the school district, and notwithstanding the fact that the terms and conditions of said sales were not fixed by the board of school directors in the motion or resolution authorizing said sales: Provided, That the terms and conditions of said sales were fixed by the board of school directors prior to the holding of such sales and that all the other requirements of law concerning the authorization and holding of such sale have been complied with.