N.Y. Comp. Codes R. & Regs. tit. 9 § 2103.4
Where, since the filing of the registration statement for any housing accommodations, there has been a change in the identity of the landlord, by transfer of title or otherwise, and no notice of such change has been filed, the successor landlord shall file a notice, on a form provided for that purpose, within 15 days after the change. In addition to any other address, the owner shall provide an actual, physical street address from which it conducts business and where the owner or an agent is authorized to accept service of documents, subpoenas or requests. In the absence of such form, DHCR may serve all notices on the last registered owner or in any proceeding where the owner has appeared whether in a rent control or rent stabilized administrative proceeding, at such address given in the proceeding.
N.Y. Comp. Codes R. & Regs. Tit. 9 § 2103.4