If you continued reading Stevenson responded to this by writing the book European Cases of the Reincarnation Type.
Doesn't negate the fact that people close to him pointed out how terrible his research practices were, and that no data he provides can be trusted because of it.
If you let the child and the family of the deceased hang out together before interviewing, you've contaminated your research. If you ask leading questions, you get invalid answers.
Not to mention there were only 40 cases. A majority of which-if not all- were children.