Second, the gold labels for the sarcastic class are obtained differently: Whereas Twitter and Reddit corpora are self-labeled (i.e., speakers themselves label their messages as sarcastic), the IAC v2 corpus is labeled via crowdsourcing.
for the latter, the gold labels emphasize whether the sarcastic intent of the speaker has been perceived by the hearers/annotators (we do not know if the speaker intended to be sarcastic or not).