With the Seltzman machine they can erase the memory back to any point in time they choose. The man lying on the operating table was extremely co-operative. He told them all they wanted to know in three days with hardly any persuasion. So then they wiped out all unhappy memories of The Village, and put him back into circulation so that he can gather more information. You see they can put the mind of their choosing into the body of their choosing. We don't know how The Village administration was able to attain a Seltzman machine. But having done so it would have taken time to develop the technique, experimentation using two "guinea pigs" at a time. I wonder how many times it took for the doctors and scientists to perfect the process? There must surely have been failures during the first experiments, subjects perhaps left with bent and twisted minds unable to accept what had been done to them. Others without the mental strength to survive the process of mind transference.