I lived for a few years within the boundaries of the European Union. As an American I was entitled to stay for 90 days, but there was a loophole.
Prior to the elimination of border controls between Schengen states, each country specified how long a visitor could remain. There would be a specified period, then, required to "reset the clock" time outside of the country before one could visit again.
After the integration of states, a person with access to one could travel between them or stay within any one with no record that they had done so. And since there was no mechanism of communication between countries vis-a-vis federalized immigration control, there was no normal way of checking how long a person had been within the newly-unionizing superstate.
At least that's how it worked for me. That's how it worked, traveling (or not) with an American passport as identification. I stayed in the Netherlands and in Spain for extended periods without scrutiny.
Nobody on the Continent knew how long I had been in their country, because they'd eliminated border controls and nobody knew how long I'd been within the EU, because that part of the agreement hadn't been worked out yet.