N.Y. Comp. Codes R. & Regs. tit. 2, § 325.3 – Tiers of membership in New York State and Local Police and Fire Retirement System.

(a) Members who last joined the New York State and Local Police and Fire Retirement System on or before July 31, 1973 shall be identified as tier one members.
(b) Members who last joined the New York State and Local Police and Fire Retirement System on or after August 1, 1973, but before July 1, 2009, shall be identified as tier two members.
(c) Members who last joined the New York State and Local Police and Fire Retirement System on or after July 1, 2009, but before January 9, 2010, shall be identified as tier three members except for those members who have opted to be covered by the provisions of article 22 on or before May 9, 2010.
(d) Members who:
1. (1) last joined the New York State and Local Police and Fire Retirement System on or after January 9, 2010, but before April 1, 2012, shall be identified as tier five members;
2. (2) joined such system on or after July 1, 2009, but before January 9, 2010, and who have opted to be covered by the provisions of article 22 on or before May 9, 2010, shall be identified as tier five members.
(e) Members who last joined the New York State and Local Police and Fire Retirement System on or after April 1, 2012 shall be identified as tier six members
Note: there is no tier four membership in the New York State and Local Police and Fire Retirement System.