IFC Version Mismatch

A version mismatch is when the IFC schema a file claims (its FILE_SCHEMA header) disagrees with the schema the file's entities and attributes actually belong to. The file is then internally inconsistent: a validator rejects it, or a reader silently misinterprets it.

ALWAYS treat the declared FILE_SCHEMA token as a contract. Every entity name, attribute slot, attribute optionality and enum value in the file MUST be legal for that exact schema.