They had come recommended to me at the time from a gentleman I used to talk with quite a bit

Lots of times the “brand” stones tend to be made for them by a stone manufacturer. Naniwa is pretty well known for this. They can, apparently, make stones to a specification. The black Kramer synthetic stones are made by Naniwa. I’ve never used them but I’m told they are of exceptional quality and not a copy of some Naniwa stone.