Postal votes are opened before the polls close and counted along with the polling station votes. No spoilt or damaged postal vote can possibly be replaced and anyway if they are spoilt, it's usually on purpose, sometimes with very rude messages written on them! It's very inefficient if the returning officer hasn't included the voting paper for the PCC in the envelope. Are you sure this isn't because the position is not being contested? It doesn't give you much time to get the papers back to the RO.