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A certification of origin is a claim. A defensible origin file is the evidence that the claim survives a verification.
When you import a UK-origin good under the TIPAT, the certification of origin is what you hand over to claim the preferential rate. The origin file is what you keep, and it is the only thing that matters if the Servicio de Administración Tributaria (SAT) verifies the claim months or years later. Operations get the first part right and the second part wrong all the time: a clean certification on the entry, and nothing behind it when the verification letter arrives.
This playbook is for the operator who has to qualify a UK good under the TIPAT and build a file that holds up. By the end you will know how to read the product-specific rule for your fraction, how to run the cumulation analysis the TIPAT now allows, who should sign the certification, and exactly which records to keep so the preference is defensible, not just declared.
Before you start
Have four things in hand. The correct tariff classification of the good, down to the level the rules of origin operate on. A complete bill of materials, listing every input and its own classification and country of origin. The origin status and supporting evidence for each input (originating in a TIPAT country or not). And the product-specific rule of origin that applies to your good, from Annex 3-D of the TIPAT.
Decide one thing up front: who will certify. Under the TIPAT, the certification of origin can be completed by the exporter, the producer, or the importer (Article 3.20). That choice changes who holds the documentary burden, and it is easier to make before you build the file than after.
Step 1. Classify the good correctly, first
Origin analysis depends entirely on classification. The product-specific rule of origin is keyed to the good's tariff classification, and many rules turn on a change in classification from the inputs to the finished good. If the classification is wrong, every step after it is wrong, and a defensible-looking file is built on a false foundation.
Classify the finished good and every material in the bill of materials. You cannot test a change-in-classification rule without knowing the classification of the inputs, not just the product.
Step 2. Read the product-specific rule for your fraction
Go to Annex 3-D and find the rule for your good's classification. TIPAT product-specific rules take one of a few forms, and you need to know which one yours is.
A change in tariff classification (CTC) rule requires the non-originating inputs to transform into the finished good across a defined classification boundary. A regional value content (RVC) rule requires a minimum percentage of value to originate in the TIPAT region, calculated by one of the methods the agreement defines. Some goods carry a specific process rule. Read the rule literally, then check whether your good meets it as built.
If your good does not meet a change-in-classification rule only because of a small share of non-originating material, the de minimis provision (Article 3.11) may still let it qualify. Confirm the exact threshold and apply it precisely; it is a safety valve, not a substitute for the analysis.
On the entry, a good either carries a certification or it does not. Under a verification, the certification is not what is examined. The file behind it is. The two are not the same document, and the gap between them is where preferences are lost.
Step 3. Run the cumulation analysis
This is the lever the TIPAT opened that the old bilateral framework did not have. Under Article 3.10, materials and production from any of the twelve TIPAT economies can count toward whether your good originates. A UK good built partly from Japanese, Canadian, or Vietnamese inputs can now count those inputs, where the prior Mexico-UK framework would have treated them as non-originating.
Map each input in the bill of materials to its origin, and identify which ones are originating in a TIPAT country. Regional cumulation can be the difference between a good that fails the rule and one that clears it. It is also the part of the analysis most likely to need documentation from your supplier's supplier, so start it early.
Step 4. Decide who certifies, and accept the burden that comes with it
The certification of origin has no mandatory format, but it must carry the minimum data elements in Annex 3-B and identify whether the certifier is the exporter, the producer, or the importer (Article 3.20). In Mexico, importer self-certification has been available since the Reglas Generales de Comercio Exterior reform that took effect on December 29, 2023, so certifying as the importer is a real option, not a theoretical one.
Choose deliberately. If the producer or exporter certifies, they hold the origin evidence, and your contract should oblige them to cooperate in any verification and to keep the records. If you certify as the importer, the documentary burden is yours, and you must hold the information that supports the claim at the time you make it (Article 3.24). For a good where you do not control the production data, importer certification is powerful but heavy. For a good you build or whose supply chain you can document, it can be the cleaner path.
Step 5. Build the file that survives a verification
This is the step the title is really about. A defensible origin file assembles, for each good and each period the certification covers: the tariff classification analysis for the finished good and the inputs; the complete bill of materials with origin status per input; the product-specific rule applied and the worked analysis showing the good meets it (the CTC mapping or the RVC calculation); the supplier origin evidence for originating inputs and the de minimis calculation for any non-originating ones; and the certification of origin itself with the Annex 3-B elements.
Keep all of it for at least five years from the date of importation (Article 3.26). The customs authority can verify a claim after the fact through written information requests and verification visits, and the answer to that verification is the file, reconstructed from memory by no one.
Common mistake: certifying a good as originating because "it always qualified" or because the supplier said so, without the bill-of-materials analysis behind it. A supplier's assurance is not an origin file. When the verification lands, an unsupported certification converts the duty saving into an assessed underpayment, plus the consequences that attach to a claim that could not be substantiated.
What "done" looks like
Done is not a signed certification. Done is a certification you could hand to a verifying officer alongside a file that proves, input by input, why the good originates, for every entry in the period the certification covers. If you can reconstruct the origin determination today without calling the supplier, the file is defensible. If you cannot, it is a liability wearing the costume of a saving.
When to bring in expertise
Bring in a customs broker or trade compliance specialist when the product-specific rule is an RVC calculation rather than a simple classification change, when cumulation across multiple TIPAT countries is what makes the good qualify, or when you are setting up a UK lane and want certainty before the first entry rather than after the first verification. The TIPAT also preserves the option to request a resolución anticipada (an advance ruling) on origin from the authority, which converts a judgment call into a documented determination before the cargo moves.
Across more than 190,000 customs operations a year at 39+ ports, the origin claims that fail a verification are rarely the ones where the good did not qualify. They are the ones where the good qualified and nobody kept the proof. The certification is the claim. The file is whether the claim was ever true. Build the file first, and the certification takes care of itself.
Talk to a Joffroy expert about an origin-file review for your UK-origin goods under the TIPAT before your first entries clear.
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