Design changes cost money, and the model knows exactly which elements changed. Compare each revision with a baseline, price the difference, and check what the quantities can't see.
Design changes are normal; surprises about their cost aren't. Because the model knows which elements changed between revisions, the cost of a change can be worked out the day the revision arrives, not weeks later. But only if the comparison is set up properly, and someone checks what the numbers can't see.
Every IFC element has a GlobalId that should stay the same across revisions. Tools compare revisions by matching these IDs: added, removed and changed elements. If an authoring tool regenerates IDs on export, every element looks new; check that first.
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