Buying property with a house blindly? Risks?

The 6m distance does not currently exist either. The neighbor is about 2.5m away.

Then you should investigate how this special case came about and not dream of being able to transfer it to successor developments. Neighbor boundary distances (each between house and fence) are usually half the height, but at least 3 or 2.5 (BW and I believe also BY) meters. They are mandatory in the respective state building codes unless it is a semi-detached house development or there is an obligation to attach. From "mandatory" also follows "to be secured," i.e., to be recorded in a public register (easement register or land register). Between both neighbors, the sum of both boundary distances must always be observed (sorry for the complicated wording, but for example, on one side there may be a low house with minimum distance and on the other side a taller one with the height formula). If one of the neighbors wishes to undershoot this total boundary distance, the other must obligatorily and documentedly assume it. Hopes for it to be forgotten after the death of the last contemporary witness are always unfounded! Setback easements can be deleted if their fulfillment is regularly secured again, i.e., if the violating building has been demolished—but they do not expire. However, current law applies—so if in Roman times two Caesars had to maintain a high distance and part of it was assumed, today it is still between 5 or 6 meters and half H + half H.