An interesting sticking point - also what I call a bit of regulatory creep (not be confused with lounge lizard or other low life).
If you go to the Type Certificate Data Sheet, which is the basis for the Certificate of Airworthiness, you'll see that there are limitations listed there. It says nothing about the normal and emergency procedures having to be followed.
So for someone to insist that the flight manual procedures must be followed would make it nearly impossible to handle modifications to the aircraft such as STCs or possibly even in the USA, form 337 changes - especially if they change the operating procedures - it would mean that literally, you would have to republish the entire procedures section in the supplement for the FM.
The FCOM, in my experience, is just a compliation of all the mods and STCs to an airframe for a manufacturer, and will contain all the required information from the AFM and supplements, put into one manual. BUt somewhere, lurking in a dim and dusty closet will be original AFM and supplements.