That World Master alto that bluespeter1 is selling on the German eBay site has been around for a while. I've had it in my gallery for at least a couple of months now under the "mystery" category. While its round thumb screw looks D&J-like, the resemblance nearly ends there. You could also throw out Hammerschmidt as a possible maker, since they used the same neck-fastening screw. (As did Hohner, but they didn't make stencils.)
Whatever this is, I doubt it is a D&J, only because of the hundreds of D&Js I've seen, and of the ones I chosen to include in the
world's largest D&J pictorial gallery, (which I'll be adding new stencil names and images to shortly BTW), there is nothing that resembles it. D&J worked in quantity to produce stencil horns that were JK The New King clones, and to a much lesser degree, Toneking copies (with a high F# key). A serial number might certainly help ID the sax, since D&J used sequential #s throughout their history, but bluespeter1 doesn't provide a number either on the eBay ad, or on the company's website....
Speaking of the company website, there they don't mention a D&J connection at all. There they just say it is from a German maker, but unfortunately further information/papers are lacking. I suspect that's a more fair assessment of the horn, since as I mentioned, the horn's been kicking around for a while. The text on eBay is the old one, so perhaps he has revised his thinking a bit when he did up his website, but just not updated his eBay ad.