Another stamp question to Gustamps

Fran Perkins asked Gustamps if some stamp errors are always discovered around the time a stamp is first issued. Fran told Gustamps she had a British Caernarfon castle £1.50 stamp with missing gold colour. Fran told Gustamps the stamp had been used. Gustamps answer to Miss Perkins was "no." Gustamps said, that although her stamp was issued in 1997 that particular error came to light in 2001.