CBP looks for a combination of supporting documentation: auction house provenance records, appraisals from recognized experts or institutions, period-consistent construction techniques noted in condition reports, and historical ownership records. Scientific dating methods such as dendrochronology for furniture or thermoluminescence for ceramics can also be submitted. No single document is automatically sufficient; a well-assembled provenance file reduces the risk of a challenge at entry.

Each article must be classified on its own merits. Furniture over 250 years old is specifically enumerated under 9706100040, while silverware falls under 9706100020, and other antiques of the same age bracket go under 9706100060. A mixed shipment requires line-by-line classification on the entry, with separate values declared for each category. Grouping dissimilar antiques under a single residual line when a specific enumerated line exists is a classification error.