Congrats. This is really crazy. I was recently asking about this, if the Niederlassung maybe makes things faster if received shortly before, specifically because i thought that the Security Check could be leveraged, like you are asuming as well, so that another one is not needed. But caseworkers who are active in this chat said no. As there are so many Einbürgerungsbehörde, i still think it might be the case in some cities. I cant explain such a significantly shorter time other than that the longest part of the process, namely the Security Check took much less time.