Sec. 3. ESTABLISHMENT AND APPLICABILITY. Subject to the authority granted the retirement board in Section 7(d) of this Act:

(1) members who retired, and the beneficiaries of members who died, prior to October 1, 2011, shall continue to receive the same retirement allowances or benefits they were entitled to receive prior to that date, together with any benefit increase authorized under this Act;

(2) members of the retirement system on or before December 31, 2011, shall be enrolled as members of Group A; and

(3) persons that first become members of the retirement system on or after January 1, 2012, shall be enrolled in Group B.