What I mentioned︀ is not an urban legend. It is a real case where the person claimed to︁ be tax resident in a tax haven while still often visiting his home country. They︂ used card statements, neighbours and highway toll gate records against him. It went through three︃ courts (local court, regional court and supreme administrative court).
This happened in 2014 and it︄ was about €4k. Let that sink in, 6 years ago, today you have better data,︅ better reporting, better technology.
I can send you the real court decision PDF if don't︆ trust me and want proof (PM me if interested) though I'm not sure if it︇ will help you as it is 10 non-English pages of law speak. He didn't go︈ to jail but he had to pay back taxes + interest + a fine.
Yes it is possible. You can never count on data being "truly deleted". The same applies to the new passenger information exchange system valid from 2019. Officially they claim that the data will be "
anonymized" after 6 months so that older information cannot be obtained, however how exactly that deanonymization looks and why keep anonymized data at all remains a mystery. Or maybe not a mystery, they just don't want to say this data will be available forever from now on.
By the way "data only available to the police" is nonsense. Usually police and state prosecutor work hand in hand (against the individual) with presumption of guilt. Only when you get︀ to court there should be presumption of innocence. What can happen is the tax office︁ automatically reports suspicion of fraud/tax evasion (the office is forced by law to report it),︂ police can investigate, police gets permission from prosecutor which is usually just a formality. Then︃ they get all the data they want.
And the situation is even worse than you︄ can imagine a) in China and b) in "golden cage" countries such as Monaco, Saudi︅ etc. Even the situation in the UK is insane, get on a bus and there︆ are 7 cameras inside.