Information Constraints, Benchmark Dispersion, and Border Misreporting: Evidence from Japanese Customs Data

Customs enforcement relies on information from comparable declarations, yet that information varies sharply across trade lanes. We link confidential Japanese import declarations to United Nations Comtrade for 2014–2021 and construct trade-cost-adjusted six-digit Harmonized System product–partner–year mirror gaps. The pooled relationship between applied tariff rates and mirror gaps is positive but imprecisely estimated. The estimated tariff–gap slope is substantially larger in lanes with few prior transactions and declarants and close to zero in lanes with thick recent declaration activity; a value-added-tax-inclusive statutory measure yields similar results. Patterns based on lagged unit-value dispersion are directionally similar, though somewhat less pronounced. On a common Comtrade sample, an accounting decomposition places most of the heterogeneous value-gap contrast in the quantity-gap component. The results document a systematic information gradient in tariff-responsive mirror discrepancies within a common high-capacity customs administration.