[fridek]

The point is - while all of these systems are fuzzy at the edges, that is not a bug. Letting people reside in a few countries at the same time, and to pick a tax residency like a new winter jacket is a non-objective for the border, tax and residency systems.

It's actually relatively simple to follow the rules that lead you down the well estabilished residency paths if you do the opposite of what the article suggests and leave enough of a buffer for every required number, so you don't need to think about it and the precise count can be handwaved by the officials.

Conversly, if you try to minmax the rules, you might find that most important systems still have an arbitrary human decision maker, who simply decides whether to apply a complex ruleset to the letter, or to be lenient.