N.Y. Real Prop. Tax Law § 1168

§ 1168. Certificate of sale as evidence. 1. The certificate of sale or\nany other written instrument representing a tax lien shall be\npresumptive evidence in all courts in all proceedings by and against the\npurchaser and his or her representatives, heirs and assigns, of the\ntruth of the statements therein, of the title of the purchaser to the\nproperty therein described, and of the regularity and validity of all\nproceedings had in reference to the taxes or other legal charges for the\nnon-payment of which the tax lien was sold and the sale thereof.\n 2. After two years from the issuance of such certificate or other\nwritten instrument, no evidence shall be admissible in any court to\nrebut such presumption unless the holder thereof shall have procured\nsuch certificate of sale or such other written instrument by fraud or\nhad previous knowledge that it was fraudulently made or procured.\n