(a) Credit for service which predates the date of entry into the system may be granted without the member being required to render a minimum of five years of credited service after July 1, 1973, provided such service is otherwise creditable, and either:

1. (1) was rendered by an employee during which employment he or she became a member of the system; or
2. (2) was rendered by an employee during which employment he or she was ineligible to join a public retirement system.

(b) Service rendered by an employee during which employment he or she became a member of the system shall be defined as follows:

1. (1) Previous service which was rendered by an employee during which employment he or she became a member of the system shall mean continuous employment with the same employer during which he or she joined the system.
2. (2) Previous service as an itinerant substitute teacher on a day-to-day basis shall be considered as separate employment for each day of such service.