New one on me, too... But, what makes you certain it's for an 1823? Could just as easily be for the 1822, and I have seen stainless Euro Calculators in this inner box (there is also a full leather-covered version of the inner box, too). And, the white outer boxes are not all that bad; I have a couple here that are quite well-fitted to the inner box.
The outer box and sleeve for the clear plastic "see-through" box for the P2 is another combination that is almost never seen.