Hi Robo so the agent says your HOUSE is legal.  Ask to see the planning permission from the Ajuntament (not the plans from the Architect).  I bet it says permission for an Almacen.
The previous Mayor was giving out permissions for 50sq.m Almacens by the dozen in 2005.  Some people got this permission and built bigger.  If however you wanted to legally build an Almacen over 50 you needed an Architect but it was still an Almacen and not a house.  Also the plans would not look anything like what was actually built. As I said previously you may never have any trouble but you should have been told the permission would have been for an Almacen not a house.  Almacens do not need a Cedular.  Would you still have bought if you had been told the truth, possibly not and that is why the Agents do not tell you.  Anyone who registered with Basa in 2005 would by now be on the maps, I know people that registered after that and their property is on the map. The majority of people have not registered to save paying the extra tax.