@Rolox,
Those (0), -3, -6, -9, -12 settings would have been based on the T2A autoformer used in Klipsch crossovers.
Al sourced the 3619 for many more attenuation options.
As Dean said, the 3636 provides many more options than the T2A as well, but many are redundant, ie. different combinations yield the same or .1 of a decibel difference. Looks like about 6 of the 28 combinations are redundant, and 4 of them are above -18db of attenuation which I cannot fathom ever needing. So each of them has 18 useful combinations?
I have never been privy to a 3619 autoformer, but I know my OCD would prefer it’s even 1 db steps.