Every person sentenced to the Department, while in a local or state correctional facility, who participates in career and technical education or other training while confined, or who shows such interest and application in his work assignment as to exhibit unusual progress toward rehabilitation, may, in the discretion of the Director be allowed a credit toward his parole eligibility date and upon the total term of confinement to which he has been sentenced. Such credit may be from one day to five days for each month he has been engaged in such career and technical education or other training or has applied himself in excess of minimal work assignment requirements. Any credit accumulated prior to June 1, 1975, toward the term of confinement may, in the discretion of the Director, be credited toward such prisoner’s parole eligibility date.