When a court of competent jurisdiction determines that a school system is desegregated, or that it meets the constitutional requirements, or that it is a unitary system, or that it has no vestiges of a dual system, and thereafter residential shifts in population occur which result in school population changes in any school within such a desegregated school system, such school population changes so occurring shall not, per se, constitute a cause for civil action for a new plan of desegregation or for modification of the court approved plan.
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Section effective on and after sixtieth day after Aug. 21, 1974, see section 2(c) of