Anything in this chapter to the contrary notwithstanding, any employee who, prior to his employment with an employer subject to this chapter, was a teacher in the public schools of this state shall be entitled to a prior service certificate for service rendered as a teacher in such public schools, provided that he filed an application with the board of trustees by May 4, 1949. Such application shall contain satisfactory evidence of such service as a teacher and a record of earnable compensation for any portion of such service rendered during the last five years immediately prior to July 1, 1949.