This is not true either: 14,000 metres is the minimum plot but there have been transitional rules which at certain times allowed licences to be issued.
Also could be license was granted before the law setting 14.000 square meters was set.
On the other hand, for some years a law called the amnesty, allowed to legalize all those constructions built without license that did not have open files of infraction. Therefore, a house built on a plot of land of less than 14,000 meters could have been legalized during this period.
Apart from what has been explained. Any construction on a rustic plot of less than 14,000 square meters is suspected of being illegal and only by checking the licenses can one know.