34 Tex. Admin. Code § 25.76
A retiree may establish credit under § 25.71 of this title (relating to Service Credit for Eligible Active Duty under the Uniformed Services Employment and Re-Employment Rights Act), if eligible. The requirements of §§ 25.71-25.75 of this title (relating to Service Credit for Eligible Active Duty under the Uniformed Services Employment and Re-Employment Rights Act; Limitations on Eligible Service; Ineligible Military Service; Cost; and Application for Eligible Active Military Duty under the Uniformed Services Employment and Re-Employment Rights Act) apply equally to a retiree establishing such credit. A retiree who establishes service credit under §25.71 may receive an adjusted benefit on a prospective basis only after such credit has been established.
34 Tex. Admin. Code § 25.76