Every FTA benefit starts with two HS determinations: the code of the finished product and the codes of its non-originating materials.
PSR rules are HS rules Product-specific rules say things like "CTH" (change of tariff heading), "CTSH" (change of subheading) or "RVC 40%". A CTH rule is only testable if both the input and output codes are correct: if your fabric is really 5407 and your garment 6204, the heading change exists; misclassify either side and the origin claim is unsupported.
Code mismatches kill C/Os at destination Import customs compares the C/O's HS code with the declared import code. Heading-level mismatches routinely lead to rejected preference, deposit collection, and verification requests back to the issuing authority. Fix the destination code FIRST, then issue the C/O to match at 6-digit level.
Verification and fraud enforcement US and EU authorities verify origin aggressively where trade patterns shift (post-301 China relocations, AD circumvention). Vietnamese authorities have tightened issuance controls accordingly. An origin file must trace every material by HS code through the transformation — the same registry that supports classification supports origin.
A practical workflow for FTA-driven business - Lock the finished-product code in the destination market (ruling where volume justifies) - Map all materials with HS codes and origins in a BOM - Test the PSR (CTC and/or RVC) with real costs - Issue the C/O consistent with the destination HS6 - Archive the whole chain — verifications arrive 1–3 years later.
Handled in this order, FTA duty savings are durable. Handled backwards — C/O first, classification later — they are a contingent liability.