I'd actually say you're dead wrong about the B-Wing/Y-Wing switch. The ROTJ-Y-Wing shot you posted appears to be the same window-shapes as the ANH-Y-Wing shot, only the camera is in front of the pilot, rather than behind, thus we see less of the side-windows. You can see the the corners of the side windows starting, however. The ROTJ-Y-Wing has struts coming up on the left and right sides of that screencap, while photos of the B-Wing model show that there really shouldn't be any struts there. The interior of cockpits may have changed, but I'd bet they got window-shapes pretty close to correct.