A look into the building permit (textual part) can provide clarification. What exactly is stated there? In NRW, it is actually the case that formally the occupancy (i.e., the use) is only permitted after official acceptance. After the so-called "acceptance," one receives a certificate if there are no defects; it is a mere formality. If everything goes well. However, if, for example, an insurance case occurs before the acceptance, I can well imagine that the insurance will like to hang up on that and refuse the settlement.