(a) Where the legal regulated rent or any fact necessary to the determination of the legal regulated rent, or the dwelling space, required services or equipment required to be provided with the housing accommodation is in dispute between the owner and the tenant, or is in doubt, or is not known, the DHCR at any time upon written request of either party, or on its own initiative, may issue an order in accordance with the applicable provisions of this code determining the facts, including the legal regulated rent, the dwelling space, required services, and equipment required to be provided with the housing accommodations.

1. (1) Such order shall determine such facts or establish the legal regulated rent in accordance with the provisions of this code. Where such order establishes the legal regulated rent, it shall contain a directive that all rent collected by the owner in excess of the legal regulated rent established under this section for such period as is provided in section 2526.1(a) of this Title, or the date of the commencement of the tenancy, if later, either be refunded to the tenant, or be enforced in the same manner as prescribed in section 2526.1(e) and (f) of this Title. Orders issued pursuant to this section shall be based upon the law and code provisions in effect on March 31, 1984, if the complaint was filed prior to April 1, 1984.

2. (2) Where either:

   1. (i) the rent charged on the base date cannot be determined; or
   2. (ii) a full rental history from the base date is not provided; or
   3. (iii) the base date rent is the product of a fraudulent scheme to deregulate the apartment; or
   4. (iv) a rental practice proscribed under section 2525.3(b), (c) and (d) of this Title has been committed, the rent shall be established at the lowest of the following amounts set forth in paragraph (3) of this subdivision.

3. (3) These amounts are:

   1. (i) the lowest rent registered pursuant to section 2528.3 of this Title for a comparable apartment in the building in effect on the date the complaining tenant first occupied the apartment; or
   2. (ii) the complaining tenant’s initial rent reduced by the percentage adjustment authorized by section 2522.8 of this Title; or
   3. (iii) the last registered rent paid by the prior tenant (if within the four year period of review); or
   4. (iv) if the documentation set forth in subparagraphs (i) through (iii) of this paragraph is not available or is inappropriate, an amount based on data compiled by the DHCR, using sampling methods determined by the DHCR, for regulated housing accommodations.

4. (4) However, in the absence of collusion or any relationship between an owner and any prior owner, where such owner purchases the housing accommodations upon a judicial sale, or such other sale effected in connection with, or to resolve, in whole or in part, a bankruptcy proceeding, mortgage foreclosure action or other judicial proceeding, and no records sufficient to establish the legal regulated rent were made available to such purchaser, such orders shall establish the legal regulated rent on the date of the inception of the complaining tenant's tenancy, or the date four years prior to the date of the filing of an overcharge complaint pursuant to section 2526.1 of this Title, whichever is most recent, based on either:

   1. (i) documented rents for comparable housing accommodations, whether or not subject to regulation pursuant to this Title, submitted by the owner, subject to rebuttal by the tenant; or
   2. (ii) if the documentation set forth in paragraph (1) of this subdivision is not available or is inappropriate, data compiled by the DHCR, using sampling methods determined by the DHCR, for regulated housing accommodations; or
   3. (iii) in the event that the information described in both paragraphs (1) and (2) of this subdivision is not available, the complaining tenant's rent reduced by the most recent guidelines adjustment.
5. (5) This subdivision shall also apply where the owner purchases the housing accommodations subsequent to such judicial or other sale.

(b)