All fruit, vegetable, grain, poultry, egg and egg products graders employed by the Board in positions in fact permanent and full-time, but who were inadvertently or incorrectly classified as temporary until January 1, 1974, shall be given aggregate State service credit for the period of employment before January 1, 1974. This credit shall be given only to persons employed on a full-time, year-round basis during which time they were classified as temporary.  Credit shall be given for purposes of determining the amount of leave earned by the employee, eligibility for and amount of longevity pay, and any other determinations for which the length of State service is relevant. Employees given retroactive aggregate State service credit under this section shall receive retroactive longevity pay, to the extent for which they would have been eligible for longevity pay if they had been correctly classified from the date of their initial employment, for all service beginning January 1, 1974, until August 1, 1977, with any longevity pay actually paid to be subtracted therefrom. (1977, c. 1038, s. 1.)