If you can consider a disbelief in God, Jesus, etc. (as I do), here's another explanation that may pop up:
You can look at the OT and pick out scriptures that make it seem like Jesus (The Messiah) was supposed to die as a ransom for all, etc. On the other hand, you can (as Jews do) look at the OT and pick out scriptures that make it seem like The Messiah was supposed to reestablish the nation of Israel, the temple, etc. Even the disciples (being Jewish) had this expectation. The earliest writings we have are at least 20 after his death so we don't have a truly contemporary record.
So, here is something to consider, is it possible the idea of "the ransom" was "new light"? In other words, could it be that the original disciples assumed Jesus was the Messiah (as the Jews expected), became disappointed when he died, and developed the idea of the "ransom" to explain his death?
Far fetched? We currently have the GB rewriting their history and beliefs as we speak. This is not the first or last religion to do so.