Should have expired decades ago - B was introduced in 1968, there's no way that would still be patented. But since it's only a simple high frequency boost/cut

Should have expired decades ago - B was introduced in 1968, there's no way that would still be patented. But since it's only a simple high frequency boost/cut it probably wasn't ever patented, just protected with trademarks to the point where if you can only call it 'generic NR' and not 'dolby B' or 'dolby C' noone would be interested. S and HX Pro were more complex, but S was rare on consumer gear, and HX Pro is more than just NR.