19. Where a decision is rendered against a party who was prevented from appearing or from filing evidence, by surprise, fraud or another reason considered sufficient, such party may demand, in writing, that the decision be revoked and that a new hearing be held within fifteen days from the day the decision is known or, as the case may be, from the time the party is no longer prevented from appearing.
A party may also, within fifteen days of the service of a decision, apply in writing for the revocation thereof if the administrator has omitted to adjudicate on part of the demand or has granted more than was demanded.