how is my due diligence statement number linked to the customs declaration

The reference number and verification number go into the customs declaration

The due diligence declaration number you receive after submitting a due diligence declaration is the link between that declaration and the customs declaration: when importing or exporting the products in question, you provide that reference number, together with the corresponding verification number, to customs. Without those two numbers, customs cannot verify that a declaration has been submitted in the EU information system for the consignment, and that is precisely what the link must demonstrate. It is therefore not about one number but about a combination: the reference number you receive after submission corresponds to a specific declaration, and the verification number confirms that the declaration is valid and accepted at that time.

This link does not concern the question of whether you submit a declaration, but rather which declaration applies to which consignment. If you maintain the same product stream for multiple deliveries, you will quickly face the question of whether one declaration can serve multiple consignments, or whether a separate declaration is required for each consignment; this also determines how many different reference numbers end up in your records and with customs. Also relevant is what happens if information changes after submission: a declaration that you amend or withdraw may have consequences for the number already used in a declaration.

What this is based on: the EU information system and the customs rules in the regulation

Regulation (EU) 2023/1115 provides that economic operators and traders submit a due diligence declaration in the EU information system before the products in question are placed on the market or exported, and that the customs authorities can access this declaration via the reference number when processing the customs declaration. The technical functioning of that register, including the numbers generated upon submission, is explained on the EU information system page for the deforestation regulation.