Although you may not be able to get a CoA maybe it is still possible to verify details with Porsche GB?
I checked my cars details with them when I bought it.
They wanted a copy of the V5 to verify I owned the car, I emailed them my cars engine number, gearbox number, chassis number and the build number under the dash pad and they emailed me back confirming all numbers were right.
At a later date I also managed to get a CoA before they were discontinued.
So at least maybe it is possible to get something back that is official?
They advised that they do not provide the correct numbers. They will only confirm whether the numbers provided match their records or not.
Hope that helps.