Okay, so I'm not all-knowing.
A few posts ago I mentioned a primocane-fruiting black raspberry, and said that I thought this was the first one out there. Apparently I was wrong, as a search of the Corvallis USDA repository turned up PI 553754 - 'Black Knight'. And that, in turn, was a seedling of something called 'Johnson Everbearing', which from the sounds of it was likely primocane-fruiting too.
The online record says it's from Illinois and was introduced in 1973, apparently by an H. Boll. Beyond that I know nothing of 'Black Knight', and even less about 'Johnson Everbearing', but I'd be interested to hear if anyone else knows anything.
That said, some of my excitement over the 'Explorer' black raspberry was warranted, in the sense that this is almost certainly a new source of the trait (since it was found in wild plants) and may have a different mechanism or inheritance.