Let us hope that it is the real thing.
I accidentally, and luckily found one russian site, and thanks to google translator, went to a LOT of other sites…by good, they have a treasure trove there! They sell regulary, and in many orchards, cultivars that are huge and hardy. I thinks black baroness was one (of course translated in russian), that is apparently Morus nigra that can take sometimes -30 celsius. Or it is a M. alba with a large black fruit.
Nevertheless, now I have to figure out how to buy plants from russia without customs entirely stopping me