We can see that although PB-train is much smaller than BC-train, the PB-trained parser outperforms the BC-trained parser by about 8% on PB-dev, indicating the usefulness and importance of target-domain labeled data especially when two domains are very dissimilar.
the gap between the ZX-trained parser and the BC-trained is only about 2% in LAS, which we believe has a two-fold reason.