24 Pa. Stat. § 542
In all cases where the indebtedness of any school district of this Commonwealth has been increased since the eighteenth day of May, one thousand nine hundred and eleven, and bonds to represent said indebtedness have heretofore been issued, and sold to purchasers for value, and all proceedings antecedent to the issuance of said bonds have been duly and regularly had and performed as prescribed by the laws of this Commonwealth, saving and excepting only that such indebtedness or increase of indebtedness was not incurred, and such bonds were not issued therefor, at the time of assessing and levying the annual school taxes, as required by the five hundred and sixth section of an act of Assembly of the Commonwealth of Pennsylvania, entitled "An act to establish a public school system in the Commonwealth of Pennsylvania, together with the provisions by which it shall be administered and prescribing penalties for the violation thereof; providing revenues to establish and maintain the same, and the method of collecting such revenues: and repealing such laws, general, special, or local, or any parts thereof, that may be inconsistent therewith," approved the eighteenth day of May, Anno Domini one thousand nine hundred and eleven; said bonds so issued, and said indebtedness so incurred, are hereby declared to be valid, and shall be held and judged to be valid and sufficient in law to all intents and purposes: Provided, however, That nothing herein contained shall validate any bonds which may have been improperly and illegally executed or sold or delivered.
24 P.S. § 542