Discorde you are correct. I joined Euroberlin in the Summer of 1989. The cbs must have known where the corridors were located as they seemed to grow inside their boundaries, I can still hear the USAF controller telling us we were 9.9nm right of the centreline , as we were avoiding weather and any further deviation would involve a Pan call
I also remember going down the southern corridor and a DDR Mig that was rolling around the corridor around us. This was before the days of tcas , but he did get very close.