This information is not entirely correct. The header of all CIS/2 files will contain:
That's the name of the CIS/2 schema regardless whether it is a design, analysis, or manufacturing model.
ASSEMBLY_DESIGN entities can also be in an analysis model so it is not a good check for design models.
Better items to look for different types of models are:
Analysis - ELEMENT entities
Design - DESIGN_PART entities
Manufacturing - LOCATED_PART entities