Facts are compiled from various standard textbooks, therefore you might find a slight difference in some facts, numbers & rages therefore when authors compile materials for the review books or explanations for the MCQ they should provide the references of the sources to prevent the confusion among students.
Sources of references shall be:
Standard textbooks (published with copyrights & ISBN)
Articles from the scientific journals (published)
Official scientific websites (universities & scientific organizations)
Sources of references should not be:
Review books compiled for exam purpose
Unpublished materials (class notes & blogs etc)
Unofficial websites (Wikipedia)
Beware: Students may perceive that the answers or the facts are wrong when he/she uses multiple materials from different coaching institutes that might lead to a mass confusion state.
The answers in FMGE are decided by references chosen by NBE & certainly not by the faculties of the coaching institutes.