Usually the other way around - state and local code amendments (additions, deletions, and additional codes) rule. 

Your state and locals should tell you what's what when you call them.  For instance in Georgia, the NFPA 101 - Life safety code supercedes sections of IBC and visa versa.  A handy dandy chart is provided in the GA ammendments to the IBC 2012, issued by the state as law.

IBC as a document has zero legal authority. It's a model code and is only law after it's adopted (with or without amendments) by the jurisdiction.

IANAL (...dat acronym tho), but in my experience smaller jurisdictions (i.e. city) within larger ones (i.e. state) can override a code requirement to make it more strict, but not more lax.

It's always good to brush up on your code with every new project. Don't trust precedent or memory, find everything in writing.