An individual shall have an employment relation to an employer on August 29, 1935, for purposes of crediting service prior to January 1, 1937, if:

(a) He or she was in the service of an employer on that date; or

(b) He or she was on that date on 1eave of absence expressly granted by the employer or by a duly authorized representative of such employer, but only if such leave of absence was established to the satisfaction of the Board before July 1947; or

(c) He or she was in the service of an employer after that date and before January 1946, in each of six calendar months, whether or not consecutive; or

(d) Before that date he or she did not retire and was not retired or discharged from the service of the last employer by whom he or she was employed, but solely by reason of a physical or mental disability he or she ceased before August 29, 1935, to be in the service of such employer and thereafter remained continuously disabled until he or she attained age sixty-five or until August 1945; or

(e) Solely for the reason stated in paragraph (c) of this section an employer by whom he or she was employed before August 29, 1935, did not on or after August 29, 1935, and before August 1945, call him or her to return to service, or if he or she were called to return to service he or she for such reason was unable to render service in six calendar months as provided in paragraph (b) of this section; or

(f) He or she was on August 29, 1935, absent from the service of an employer by reason of a discharge which, within one year after the effective date thereof, was protested to an appropriate labor representative or to the employer, as wrongful, and which was followed within ten years of the effective date thereof by his or her reinstatement in good faith to his or her former service with all his or her seniority rights.