It doesn't work easily and automatically. There is still no implemented cross-border-shared, Schengen-wide entry-exit database tracking applicable to EU member state citizens or even non-citizen/non-national, long-term residents. This kind of thing comes up often when say the Danish authorities are trying to calculate the claimed physical presence of Danish residents who may have a lot of their entries and exits into the Schengen zone take place via non-Danish, Schengen ports. If the Schengen entries and exits aren't all via flights from the same country's national entry-exit system and some or much of the travel doesn't involve flights, then the electronic records are even more fragmentary.

There is also still no implemented cross-border-shared, Schengen-wide entry-exit database tracking applicable to third country nationals when a visa is not involved.

Even as just a US citizen, the Schengen countries' port authorities have a very fragmentary understanding of the duration of my physical presence in the Schengen area and often default to using the stamps to try to determine physical presence because the way I travel rather often circumvents the ability of any given Schengen country's national entry/exit database to keep track of my trips. Only after the EU/EEA gets to using the still-under-development Schengen-wide entry-exit system and no longer need to rely upon stamps, then maybe eventually they will get around to also tracking EU/EEA citizens via this still-under-development system or something like it.

https://ec.europa.eu/home-affairs/e-...-system-ees_en