When the in-domain sample is reduced to 100 sentence pairs, the LM-based methods only get a small improvement over the baseline, while the "ohcnn" got a 1.2 BLEU score improvement over the baseline and "sscnn" got a 2.1 BLEU improvement over the baseline.
even if we have no domain knowledge about the training data, when we have only 100 sentences in the test domain, the semi-supervised CNN classifier can still select a good in-domain subset and achieve good performance.