Don't worry about the various different systems some were based on Kodak filtration and other Agfa etc look in an Ilford Multigrade datasheet they give the filtrations for the various systems.

All that matters to you is if you dial in 10y 10m 10c you get a degree of ND filtration, 20 or 30 of each is just greater ND filtration. My M601 and CLS66 is in storage (it's a spare now) or I'd tell you exactly but very roughly 10y 10m 10c should be about 1 stop and so on.