Yeah, I have the grey glass bottle, the clay bottle labelled Zeer Oude Genever, and I also have a clay bottle of Bols Corenwijn
I would guess the Bols Zeer Oude Genever has a pretty high malt content as well. If you have the clay or "stone" bottle it is pretty old as those changed to brown painted glass about 10 years ago.
As I understand it Corenwijn is supposed to have at least 51% malt wine as compared to the at least 15% requirement for oude genever. But since Bols has at least 51% in their genever anyway I was never quite sure what the distinction was. Maybe it has even more malt wine content than the Bols genever. I do rather like the aged Corenwijns. I have a Bols 10yo that is quite tasty neat. A lot of places suggest refrigerating or even freezing it like gin but that is just a waste to me.