Who hands it over matters less than what it becomes once handed. In an importer's file your declaration becomes a comparison set: your value against their declared value, your description against their classification. The notice asks outright how to treat differences between the price reported to a foreign authority and the US customs value. Those differ for honest reasons, and in three years you are the only one who can explain why. That question lands in Ireland too.
Not overthinking. The clause is premature though: entry, records, or on request are all still live. Write the retention line now.
What it becomes once handed is the part I had not got to, and it changes what I write.
Our export declaration carries a border value: freight and insurance count only as far as the frontier and nothing past it. US customs value is the price paid for the goods with international transport and insurance taken back out. So on a delivered sale one invoice yields two customs numbers and neither of them is the invoice total. That is the first honest reason. The second is later credits. When a price is adjusted after the goods have gone our declaration was filed long before and is not reopened, and I understand the US side disregards a decrease agreed after import in any case. Two systems both correct, one difference to explain.
Which makes the retention line easier to write and harder to satisfy. Holding the document proves nothing on its own. What has to survive is the term of sale, what sat inside the price, and who priced the cold chain, because in three years the file will not explain itself and the person who could has moved on.
I still cannot see how long to say. The notice asks itself that question too.