This happened quite a lot in the 80s. It was your responsibility to take the escritura to the Registry but probably no one told you. Try taking it now – if no one else has registered a later title, then in theory they should register it. If not, try to find a good local gestor. Failing all else you will probably have to apply to the Courts for an “expediente de dominio” to register a possessory title, which you fortunately appear to have (30 years’ uninterrupted possession).