Aggravated by the partial double-blind character of the challenge, it can not be strictly ruled out that a training or test set member has to be removed completely from the challenge, because experiments or their interpretations reveal a major problem. Such problems may include the discovery of new monohydrate or even monomer conformations which complicate an unambiguous assignment , issues with the cluster size assignment, experimental downtimes due to instrument failure, commercial availability bottlenecks, etc.. However, we expect that such problems do not exceed a 10% threshold and thus do not significantly narrow the significance of the challenge.