I also recently acquired some old paper from kentmere, though somewhat indirectly as it was sold by luminos which rebranded and sold the kentmere paper. It was Charcoal R warmtone on a wonderful watercolor paper base. I checked for base fog by tossing a piece of it directly into fixer, and another into developer and processed normally. Luckily no fog at all on the surface, though the very cut edge of the paper did show a little darkening. It was really slow though but made a nice print. Unfortunately lots of cool and odd ball papers with the huge variety of surfaces seem to be gone for good, and wont be made again short of coating it yourself with liquid emulsion which is quite sad.