"AFM" is the formal regulatory term for the document which contains the authoritative information/limitations, by which the aircraft must be operated. "POH" was often the term used by Cessna, and there was a statement in the front stating that the POH was the document by which the aircraft was to be operated, as there was no more formal equivilent.
Though the POH or AFM might contain sections whoch are referred to as "unapproved", that's a regulatory thing, and it does not mean that the referenced information is not the most authoritative. A manual for an aircraft which contains pages marked "unapproved" is a sure sign that other pages in that document are approved.
Though errors can, on rare occasions, be found, these documents are very carefully worded as to their authority.