How then can you compare anything it says to anything that happened in the real world and then make that a basis for attestation?
Because the Great Revolt DID happen and the Romans DID sack and burn the city of Jerusalem in 70 AD.
Mark, in the guise of a "prediction" recounts the destruction of the temple. That's the start point...the earliest date when his story could have been written. Ignatius mimics the observations of "Mark" regarding Pilate and Mary and such and was executed c 107 AD. I'm following Doherty's theory that 'Mark' was first to lay this story out and that means that Ignatius' ideas had less than 40 years to develop. The ideas that Ignatius lays out are the basis for the literalist interpretation so that is the latest date.
Pliny gives us no idea what the group he questioned believed in. He tells us what they did not what they thought which he unfortunately dismissed by referring to it as "pernicious superstition." Had he elaborated a bit we might have known if he was dealing with a literalist or a gnostic group. But he didn't and we can only work with what we have.