The BPC had a small portal window over window 2 giving only the CDR a clear view. There are a few diagrams of it. Not sure why, but I guess in case the IU failed. Gene Cernan remarked in "In the Shadow of the Moon" that the CDR could have flown the stack into orbit using only the stars.
I thought only the hatch window was visible through the BPC, and not the rendezvous window. But I guess there were 2 windows through it? I never realized that!