Difference between "Core Classes" & "Campaign Classes"

Hello all, my first post on the forums.
Just downloaded my PDF version and signed up as a Conqueror for the Players companion. Excitedly skimming through the core rules PDF and have my first question.
What is the difference between a “Core” Class and a “Campaign” class?
I’ve read through the description of classes on pg:18 but see no mention of the differences, if any?

My take on it…
The “Core” classes are the classes you can expect to see in just about any ACKS game, regardless of setting. Disallowing one of them would drastically change the game dynamic.
“Campaign” classes are more setting specific. A GM could reasonably say “Yeah, there are no Bards or Assassin in this setting” without rocking the world to its core.

Luftmensch nailed it.

Thanks for the clarification