you just can not compare any "independent" consulting, or institution, or whatever because:
1) they are never independent, you cant picture a bunch of people isolated from a society and worst, if they are involved in politics by publishing numbers. They occupy a position of power, of political power, always.
2) they never ever will have the resources (money, people, methods, logistic, etc, etc, etc) the official data has.
So I would say that official data is -por default- the most reliable information.