There was absolutely nothing in NATOPS concerning the bunks, at least not through 1996 when I last had the manual. It was something the pilots and FEs would always say but it was never there. Wishful thinking?
The only thing is that they're referred to as the Pilot and FE racks in NATOPS, but doesn't say it's only for them. Twisting of NATOPS verbage? That would never happen.
Four pilot flights suck for rack rationing, however I found the galley seats to be just as effective, assuming the IFT and someone else hadn't already occupied them. The worst is when you're at max capacity and full of cargo, then space is really limited.