Checklists...
Good post and maybe I can help illuminate things.
EU OPS requires AOC holders to develop their Operations Manuals, of which the most relevant to this discussion is Part A and Part B.
Part B deals with the checklist issue. The operator can generally accept the manufacturer's checklist for their own use however; the checklist cannot be less restrictive than what the manufacturer has developed. i.e. The Operator can place "Cabin Attendants.......Advise", in the Before Takeoff Checklist, if that is not in the manufacturer's checklist, but not remove 'Flaps.....Set' if the manufacturer's checklist contains the item. There must also be a reference to the use of checklists in Part A, thus both Part A and B become further related.
To maintain a Quality loop, the Checklists must have a serial number or reference to the Part B. This then makes the Checklist, a Controlled Document. When the Authority receives the AOC documents for review during the course of its review, these references and checklists are assessed and the manuals are then approved.
The same goes for MELs.
What is NOT legal is checklists and 'aide-memoires' that pilot's and crew 'make up' and use in the daily course of our work on the flight deck. Even though some of them are excellent, each of these documents need to be 'controlled' by the Quality department.
The reason for the foregoing is that in case of an incident or accident, the investigation will undoubtedly swing around to cockpit procedures. If it is found that the crew were using or there were uncontrolled documents found in the cockpit, the legal aspects become very interesting.