Yup, essentially we went too far up and to climbers right until we reached a point where we couldn't go any further without climbing some truly dodgy stuff. In hindsight that wouldn't have helped anyway as the buttress is detached with BC running behind it.
Even from the top BC is still pretty tricky to find, with a number of false trails and dead ends. It's the kind of mistake that seems hard to make once you know the setup but easy enough to do at the time. In particular we got a bit fixated on the beta that talked about doing "down and right" from the top of the P4 ledge.