You just confirmed that it is being used and that it has useful data. Studying it are using it and as you bring up it has been used to prove that his conclusions about twins where wrong. In fact his data proves the exact opposite, that twins separated at birth do not show similar intelligence and school results.
Of course thats not the use he intended but it's still useful.
Huh? Mengele's twin research had nothing to do with intelligence of twins separated at birth. It involved mutilating twins (e.g., injecting chemicals into their eyes to try to change the eye color) or killing and dissecting them.
There was no systematic scientific design. Just sadism pretending to be science. What useful information, intended or unintended, has anyone found in his data?