I find it hard to believe there is signing off and issuing of fire certs without inspection? Are you sure it is based on plans
If a firm of architects have signed off a fire safety certificate that is false are they not liable ? Don't they have insurance for such eventualities.
I'm not 100% sure how the issue came to light. Was it the council? What is DFB? Was is a structural engineer looking at the building for a potential buyer? Was it a resident/owner?