Interesting subject. When I was with SQ years ago on the B707, the AOM was straight Boeing with an SQ label on the front cover. Of course it was a relativly small company then (16 aircraft). As companies develop and add more aircraft, management "adjusts" the manual for their operation, often every time a new Chief Pilot takes office. This CAN be quite a big problem in the long run. IMHO, the procedures offered my the manufacturer should be followed if at all possible. After all, they DESIGNED it.