For what it's worth, the issue of legitimacy is directly touched upon in the
Gospel of Nicodemus. In that Gospel certain Jews charge that Jesus was born
of fornication. Jesus' supporters in turn point out that Joseph was
betrothed to Mary before the conception and therefore he was not born of
fornication. No mention is made of virgin birth.
The Gospel purports to be an official record of Jesus' trial. Justin in fact
claimed that such a record existed. The prevailing view, however, seems to
be that the Gospel was written in the third century. Whatever the case,
apparently there were some early Christians who, while not believing in the
virgin birth, believed Jesus was a son of Joseph conceived after the betrothal.
With kind regards,