Double checking taxonomy of cerithium

[wateryworld]

See, that's not really helpful to me.  One source says one location, another a second location, how is that any different/less confusing than them saying two different names?  How do I know which one is wrong without having to learn EVERY SINGLE THING about each species?  And animals are mobile for the most part, many can pick up and move to another location over time if they feel like it, and be in more than once place at once... ???

My stercusmuscarum is labelled as being from the gulf of California, while the vertagus is labelled as "West Pacific" (yeah, that's real specific)