This is fine until an auditor opens the file years later and asks not when the notice appeared but what the exporter could actually check. The gap becomes yours the moment a claim rests on a South African material, because that exclusion list was unreadable in the weeks the statement was made. Nobody reconstructs that later from memory. I would rather go back with a fresh statement and dated supplier evidence than defend a blind one, even though it looks like admitting a problem. A correction you file yourself survives better than one they find.
Agreed on going back rather than defending the blind one, with one caveat from my side of the trade. A fresh statement can be written today. The papers that put the box in those weeks cannot: the loading and transport records are already dated, and nothing you do now changes them. So pull those first and tie them to the marks and numbers on the packages, then hang the supplier evidence off that.
At my port, the material supplier is usually the part that has moved on. Lots get renamed, people leave, and a declaration nobody can trace back to a batch is just a letter.
I would be the one told to rebuild that file, so from this end: the material half of it sits here, not in Germany. Whether a South African material was on the excluded list is answered by a supplier on this side, and that list reaches us through its own channel and is published under our own procedures, so what was readable in Johannesburg may not be what was readable to you.
Nobody here reopens a shipment nobody queried, so I would ask now, in writing. Otieno is right that some papers cannot be written later; a dated question to a supplier is one that still can.
I sell knitwear into Europe from inside a customs union, which is not a free trade agreement, and the thing I explain most weeks is that the paper proving goods are in free circulation proves nothing about where they came from. A rule turning usable before anyone can read it is familiar from that side too.
Both of these stop on the export side of the file, and that is what I would add to. A fresh statement is yours to make. The entry it belongs to is not. Once the buyer has cleared the goods, nothing you write reaches that entry: they have to go back to their own authority and ask for it to be re-opened. That is where it stalls. A German buyer of mine last spring weighed the duty at stake against the amendment and said plainly he would rather leave a cleared file closed than invite anyone back into it.
So ask the buyer first whether they will use what you write. If they will not, build the file to defend the claim that was made, not to replace it.