Strictly speaking that's insufficient as crossing from the US into Canada by land doesn't invalidate your I-94. They do need to join it against a bunch of other data -- which they do have.

Exactly. They have the data, but they’d need to link it to a few other sources for it to be complete.

The US, unlike Europe (at least in my experience) doesn’t check passports on the way out. They rely on flight manifests or information from Canadian authorities on who has exited.

> unlike Europe

Unlike the Schengen zone, certainly, but some European countries also do not check passports on exit (the UK is a good example).

Bosnia just waived me on when I was crossing through from Croatia. Checking a whole buss must have seemed like too much effort

Yup. It was Schengen in my case.

With so many types of data collected, one shudders to imagine what will happen if they discover the join sql statement.

When did they add the join statement to COBOL?