Approved Inspector cannot find Building Regs Completion Certificate

AstroFan

I'm selling my house.  The Council have confirmed that there was a Completion Notice recorded for the original build in 2009 and that I should ask the Approved Inspector (name and address provided) for a copy of the certificate.
But the Approved Inspector says they cannot find or have no certificate on record.
The property was one of 4 on the same planning application and development.  One of the other houses even has the same Completion Notice date.  The Inspector says they only have completion notices for the other three.
The Inspector inspected the property last week and verbally noted that all was built according to the regulations fwiw.
If the Inspector continues to say they don't have the record/certificate, or won't provide/reissue a copy, what are my options?  (Is there a law that they must maintain their records for 15 years and provide a copy completion certificate on request?)
Is Council Building Control confirmation of the Completion Notice on a specific date good enough, without the actual piece of paper?

Background:  The original owner has since died and our conveyancer clearly did a poor job when we bought as this document was not in my records from the purchase (they have since been wound up).

propertyrental

Council must surely have a copy? How did they confirm it was recorded? Can you get a written confirmation from council?

user1977

I'd be satisfied if the council have it noted as being signed off, given the main (theoretical) risk is the council taking enforcement action due to it not being signed off...