(a) In the event a member of the public system has served in a position prior to the date the teachers' system was created, which position would be covered under the teachers' system as of the date of retirement had the teachers' system been in existence at said time, the board of trustees of the public system may grant said member prior service credit for said time worked under such rules and regulations as the public board may from time to time adopt.
(b) In the event a member of the teacher system has served in a position prior to the date the public system was created, which position would be covered under the public system as of the date of retirement had the public system been in existence at said time, the teachers' retirement board of the teacher system may grant said member prior service credit for said time worked under such rules and regulations as the teacher board may from time to time adopt.