That’s the whole point of preregistration. The nine unpublished trials can be assumed to be negative, or at least neutral, and were aware that they were done because of preregistration. Therefore regulators have the ability to reject the notion of the effectiveness because so few of the studies reported positive outcomes. In addition, any cancelled studies now taint the authors and sponsors with a (small) amount of suspicion that they are refusing to publish non-positive effects which, cumulatively, will cause their results to be further discounted. That will hopefully provide a strong incentive to publish neutral and negative results.