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Actually, the Mercenary Merchants will tell you which arcs you have done, but the actual void progression doesn't matter for specific mission arcs. In other words, finishing any mission arc will get you to voidb (the name of the zone when you zone into the void and do a /who command), finishing a second arc will get you voidc and so on. But specific arcs unlock certain tiers of mercenaries. Oceangreen = T2, Kithicor = T3, etc.

Here's the SoD progression guide link:
https://everquest.allakhazam.com/wiki/EQ:Seeds_of_Destruction

I'm not too up on the UF as I haven't been playing much the past several months, but here's the link to the progression guide:
https://everquest.allakhazam.com/wiki/eq:Progression_Through_Underfoot

An alternative and widely used source for modern EQ progression:
http://home.comcast.net/~mathadon/Guides/index.html

Yther Ore.