These studies are very flawed for several reasons, the main one being "separation" which is a very loose definition of separation. If identical twins grow up together but some time in childhood one is sent to live with a relative, before a later reunification, this is called "separated". It does little to separate nurture from nature.

Which makes sense - how many identical twins are separated at birth? Even if they were, it is unlikely one would be sent to Cambridge and one to rural Nepal (one of the lowest places for these IQ studies).