The problem isn't that the GPS is wrong, the problem is that the user is in error. In the Iceland case, the driver made a typo and wound up going to a similarly-named road 250 miles away. Had he entered the correct street name, he would likely have made it to his destination without a problem. I'm guessing the Belgium-Croatia case is similar.
The nav system can be in error if there has been recent construction. We tried to route in a rental car in San Diego to a restaurant and it got us looping infinitely in a little area where new roads had been lain but nonew buildings.