Every time I leave Australia, I have to fill in an official form that the government collects to state that I've left the country.
However, when I left the US last week (after my first visit there), at no stage did anyone official verify that I was leaving the country. I checked in at the QANTAS desk at JFK and passed through TSA security there, and that's it. I got on a plane to LAX and then from LAX I didn't go through any checkpoints, and left the country. No immigration, no nothing.
Does the US government know that I've left the country?