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does a 0 value for global bump affect the bump value/map set in the in the bsdf of that material?

No, it only affects the map set in the global bump slot. I think it would be pretty rare to use bump in individual BSDFs with 2.0 - pretty much, I'd only do so when making a stacked material that uses masks - I might want bump on one portion of the surface, but not on the rest.