This is a non-issue. Of course the government won't know everything for everyone. That is the reason you get the chance to make changes to your return. And even

This is a non-issue. Of course the government won't know everything for everyone. That is the reason you get the chance to make changes to your return. And even then, it'll still be a little easier than doing the same return in the US. Even with a system of "not so many details", a few things are simply going to slip through the cracks but this isn't going to affect most people.