Thats you call then, However there is not a hope in hell id be issuing a EIC for somebody else's work. For Example. What would happen if the cables are not in the correct zones and the next homeowner puts a nail through the cable the RCD fails and they die.. Your signing to say its your work and if it end up in court well..
I know this is the worst case scenario but as i say i will allways only give a cert for work i have done. I did do a unfinished house once where everything had been wired, Just required second fix and board and test. Issued EIC however clearly stated that the existing wiring was already there and therefore only responsible for the work i have installed