I think that the WPI sent Kuppeweld positive samples and it was these that he tested to validate his technique. However, the WPI letter does state they received samples from Kuppeweld in which they did detect XMRV. This implies that Kuppeweld's technique was able to find XMRV in the WPI's samples but not in his own. It also implies that the WPI was able to find XMRV in both their samples and Kuppeweld's. The question is now: did Kuppeweld include the samples he sent to the WPI in his own study?