Undercutting the boundary distance of 3 m

rn I would therefore ask to give statements only from corresponding personal experience or professional knowledge.

You are shooting yourself in the foot with the only member who has the "professional experience" you demand and who has still given you a valuable answer based on it? Impressive...

My questions: 1) What is the usual further procedure? That is: what does the building authority do with the measurement protocol? File it and possibly wait until the neighbor "complains" or do they become active now? If yes, to what extent?

Usually nothing happens. Even experts have no experience with the opposite case because it hardly ever occurs.

2) Are there possibly "building tolerances" within which deviations are accepted?

2) Not explicitly codified. But the 2cm are within the tolerance of a cadastre as old as explained to you.

3) How could the grievance – if necessary – be remedied?

Compensation payment or dismantling.

Thank you for your understanding. :)

Please. It's not a problem if you lack understanding for helpful contributions. What is a problem is discrediting those who provide answers instead of asking questions.

As pedantic as you come across here, I hope you get the same kind of officials who demand the removal of the 2cm.

I sign immediately

By the way, you can’t see the job titles in portrait mode on a mobile phone, only when you turn the phone sideways ;)

Personally, I think it’s good for neutrality :)
However, it is quite funny how some “correct” answers are rated here.

When it comes to experiences with the authorities: every builder has a different experience, worse is that the same behavior from the authorities can be perceived differently by different builders, leading to two different answers ;)