What are product-specific rules of origin?

Every trade agreement has a long list of rules, one for each kind of product, keyed to its tariff code. To claim the lower rate, your product has to meet the rule for its code.

What a rule looks like

Most rules ask for one of three things. The imported materials have to change tariff code when you make the product. Or the imported materials can only be worth so much of the product's price. Or a particular step has to happen in the country, like weaving the fabric or a chemical reaction.

Plenty of rules give you a choice of two, and you only need to meet one. A product that is wholly obtained, or made entirely from originating materials, doesn't need its rule at all.

Why the code matters so much

The rule is looked up by the product's code, so a wrong code means you're checking against the wrong rule. And the same product can have a different rule under each agreement, so it can qualify under one and not another.