If the sin of disbelief is unforgiveable, why even say to the Pharisees, who had the benefit of hearing HIM, and acknowledging HIM...even if at that moment they did not believe, afterwards, when it was noted that HE had risen, those who still continued in disbelief, would die in their sins...with no possiblity of being given a second chance because they had a FIRST chance to begin with.
But these who died prior to HIS first coming, did not even have a FIRST chance to hear THE GOSPEL preached.