The reason for this is that diagnostic examples were selected for a broader range of topics (not only politics or sports).
document context sentences (DCS) contain 364 unique entities of which only 47 appeared in an exact word form in the training data, and only 42 of them have the same entity type (organization, location or person) -the same type as in the CoNLL 2003 Stanford CMU ELMO FLAIR BERT Figure 4: Radar plot with the strong and weak sides of NER models.