N.Y. Surr. Ct. Proc. Act § 1710
A person shall not exercise within the state any power or authority as guardian of the person or property of an infant by virtue of the appointment by the will of an infant's parent, being a domiciliary and dying after this act takes effect, unless the will has been duly admitted to probate and recorded in the proper court and letters of guardianship have been issued thereon; or by virtue of an appointment contained in a deed of the infant's parent, being a domiciliary, executed after this act takes effect, unless the deed has been acknowledged so as to entitle it to be recorded and has been recorded in the office for recording deeds in the county of domicile of the person making the appointment at the time of execution thereof.
N.Y. Surr. Ct. Proc. Act Law § 1710