Boundary construction / boundary wall and property boundary

I will ask questions.

Then also ask right away whether the border has been established.

there probably hasn’t been any reason for 100 years

What reason is there after 100 years to clarify the ownership question of an airspace? Is it exactly 100 years or could it also be 124? I ask because at least in the Prussian territories qualified boundary surveys including the existing buildings were regularly conducted from 1896 onwards. Before that, there were also surveying regulations, so in individual cases one can still find something.