FDMII:
I don't know why but, FWIW, the Boeing FCOMs in general are notoriously poor by comparison with other manufacturers' FCOMs in providing aircraft technical information for flight crews, so misconceptions are bound to occur.
Then again, major airlines, at least in the US., do not (or did not during my tour of duty) use Boeing's or other OEMs FCOMs. They wrote their own, tailored to their training methods, and with FAA concurrence.
The concept worked great at TWA. TWA called them FHBs, for Flight Operating Handbook. So, whether it was a 707, 727, 767, DC-9, MD-8x, L1011, all the FHBs had "that familiar appearance."