It seems a bit naive of the government to reveal to you your income sources they know about. If you have any hidden ones you can confidently not report them and pay less taxes than you would otherwise.
It's the same in Denmark and it feels right to me. It's not like they are doing detective work (per default). If you have a concealed source of income, I'd expect them not to know about it. Of course, you'd still be breaking the law by not reporting it and it could turn up if they notice something that doesn't add up somewhere.
I assume this would still be a crime, and you'd be held responsible for lying on the past forms in discovered. The only difference is, this is optimized for making the common case easier - the case of typical income of regular, honest individuals.
Do note that it the responsibility of the employer to report who is employed, so if anything is missing, then it will generally be the company that is the one in the wrong. Especially as the company also pay employer fees for employees, so it would be a flagrant case for the tax agency anyhow.