There is lots of inaccurate information being pedalled about entry requirements into and out of the EU on various book of faces groups, irrespective of any stamps, smiling sweetly at the official, waving your arms saying no espanol or other lane reasons, every time you book a flight/travel you provide API this information is stored on both a local, regional, national and international system which all agencies have access to. You overstay by one day and the system knows, but this only works when it works so manual checks require the stamps. Check the data people are being both fined and then barred around the world.