NTCS is not a fail. It is an observation. Nobody is obliged to rebuild their house every five years to match the latest standards, whether this is removing thatched roofs or leaded lights, or having twenty sockets in your kitchen. There might however be points which are unsatisfactory or need immediate action or are dangerous, and some which could be made more convenient. Quite likely the earthing will benefit from being upgraded but it is unlikely to be obligatory.