N.Y. Real Prop. Law § 316
Each recording officer must provide, at the expense of his county, proper books for making general indexes of instruments recorded in his office, and must form indexes therein, so as to afford correct and easy reference to the records in his office. There must be one set of indexes for mortgages or securities in the nature of mortgages and assignments of rent; and another set for conveyances and other instruments not intended as such mortgages or securities, and executory contracts for sale, purchase or exchange of real property, or memoranda thereof, and instruments canceling or extending such contracts. Each set must contain two lists in alphabetical order, one consisting of the names of the grantors or mortgagors and assignors, followed by the names of their grantees, mortgagees or assignees, and the other list consisting of the names of the grantees or mortgagees and assignees, followed by the names of their grantors, mortgagors, or assignors, with proper blanks in each class of names, for subsequent entries, which entries must be made as instruments are delivered for record. This section, so far as relates to the preparation of new indexes, shall not apply to a county where the recording officer now has general numerical indexes.
A recording officer who records a conveyance of real property or assignment of rent, sold by virtue of an execution, or by a sheriff, referee or other person, pursuant to a judgment, the granting clause whereof states whose right, title or interest was sold, must insert in the proper index, under the head, "grantors" or "assignors", the name of the officer executing the conveyance, and of each person whose right, title or interest is so stated to have been sold.
Such indexes shall form a part of the record of each instrument hereafter recorded.
A county clerk may adopt a new indexing system utilizing electro-mechanical, electronic or any other method he deems suitable for maintaining the indexes.
N.Y. Real Prop. Law § 316