Another important point is that in the NAIST Text Corpus, if the antecedent of a zero anaphor is not explicitly written in the corpus, it is simply annotated as 'exophoric', and the subject sharing relations between two predicates whose subject was annotated as exophoric cannot be captured.
in our cleaning procedure, the annotators additionally annotated such 'exophoric' subject sharing relations to take into account all subject sharing relations in the corpus.