Having mulled it over a bit, on reflection, it is not incoherent for Spain to apply the rules on non-Schengen states only. The purpose of the transmission of API data is primarily to combat illegal immigration rather than for security purposes. By definition, somebody who has been lawfully admitted to the territory of a Schengen state would have the right to enter Spain (except for some very limited exceptions). This would not necessarily be true, however, of somebody entering Spain from a non-Schengen state (ie: UK, Ireland, Bulgaria, Romania and non-EU states other than Iceland and Norway).