(a) Eligible employees may make an election under subpart D of this part on a form prescribed by OPM and filed with the employing agency.

(b) For elections of retirement coverage under subpart D of this part, the election form will require that the employee obtain a certification from his or her previous retirement system showing dates of service, amounts transferable from the previous retirement system to the elected retirement system under subpart E of this part, and that the employee became vested in the retirement system. If an employee was covered by more than one retirement system, he or she must obtain certification from each retirement system.