Seal number: the field that is allowed to change

A seal number is the number on the security seal fitted through the locking bar of a loaded container’s doors. It is recorded when the box is stuffed and then copied onto the paperwork, and its job is narrow: to let whoever opens the container say whether the doors were opened on the way.

It is the one field on an import document pack that is allowed to be different at the other end. That is the thing to know about it, and almost nothing written for importers says so.

What US law does with it

Two provisions, and they pull in opposite directions in a way that is useful rather than contradictory.

The arrival filing has to carry it. 19 CFR 4.7a(c)(4)(xiv) lists “The seal numbers for all seals affixed to containers” among the elements the carrier files on the Cargo Declaration, alongside the container number at (c)(4)(xiii). The plural is in the regulation twice: all seals, all containers.

And the seal is allowed to come off. 19 CFR 18.4(a)(1) sets the baseline, that seals “remain intact until the merchandise arrives at the port of destination or the port of exportation”. Then 18.4(c) names the exceptions: where it becomes necessary in transit, “a responsible agent of the carrier may remove the seals”, including “because of casualty or for other good reason” and “when required by law enforcement or another government agency”, and the agent may reseal afterwards. The sentence that follows is the one a desk needs: “Updated seal numbers must be transmitted to CBP pursuant to § 18.1(h).”

Why that changes the checking rule

A document check that flags every seal-number mismatch as an error is wrong, and a check that ignores them is worse. The two cases look identical on the paperwork and they are not the same thing.

• The seal was lawfully replaced, and an updated number was transmitted. The file is complete; what is missing is the update on your copy.
• The seal was replaced, broken or never fitted, and nothing was transmitted. Now the only evidence that the declared cargo is the cargo that travelled has gone.

So the question to ask is never “do the numbers match”. It is “if they differ, is there a transmitted update that accounts for it”. That is one phone call at the time and an unanswerable argument six weeks later.

Why it matters more than it looks

Because of what a seal does to every other document. 19 CFR 4.7a(c)(4)(vii) requires, for a sealed container, “the shipper’s declared description and weight of the cargo”. Nobody between the stuffing and the delivery opened the box, so nobody in between can describe what is in it from their own knowledge. The whole carrier-side record of your consignment rests on what the supplier wrote down, and the seal number is the only field on the file that says the box was not touched after they wrote it.

That also makes it the earliest field you cannot verify yourself. It is set at the far end, by the party you are already chasing for the packing list and the invoice, and it reaches you on their paperwork or not at all.

What Docket does with it

It reads the seal numbers off every document in the pack and compares them, the same way it compares container numbers, and it treats a difference as a question rather than a verdict: which document says what, on what date, and is there a reseal in the record. The point is not to catch the supplier out. It is that the answer takes a minute while the box is still on the water and takes a week once it has landed, and a container waiting for an answer is a container on somebody’s storage clock. Document packs routinely run about eight days late against free time, and a week of demurrage on one container has cost US$12,000.