In England at least, energy performance certificates are widely faked. Anything the inspector can't verify they are allowed to estimate. So you get things like "I'm afraid the curtains are closed now, so we can't see the windows, but I estimate they're double glazed".
Ah. So basically a multi-tier building code that builders/etc certify during their work? Makes sense - I'm not sure if there's an equivalent in USA or not. There are certainly minimums in most/all? places, but I have no idea how much consistency there is. The bigger problem is probably that there are a bunch of old, cheap buildings in places that experienced major housing booms during lax requirements, and those still exist :|