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 sale 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 over the exact period of time prescribed by law 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 notice of such public auctions was published in one or more newspapers of general circulation published within the county or the school district for at least three times before the date fixed for said sales, each time being in a different week, and providing that the terms and conditions of said sales were fixed by the board of school directors prior to the holding of such sales, and providing also that all the other requirements of law concerning the authorization, advertising and holding of such sale have been complied with.