The "Catholic Bible", whatever that is, does not include dating of letters. For the discusson of decievers, read this article and the one on docetism. Justin Martyr is not saying that Jesus is a "myth" in the sense that he wasn't real. He is saying that what Christians say about Jesus should not be unbelievable to people who don't find it difficult to believe that Juptier had sex with human women and gave birth to real physical people who were demi-gods.