Unjust enrichment doctrine not bar to refund of duty paid under protest; provisional assessments preserve refund entitlement.

The doctrine of unjust enrichment does not bar refund claims for duty paid under protest; recoveries or refunds consequent on final determination of duty liability fall outside bars that would deny restitution. Provisional assessments and unresolved price and classification lists render clearances provisional, supporting the taxpayer's entitlement to have refund claims adjudicated on the basis of final liability rather than dismissed as struck by unjust enrichment.

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