Vaticinium ex eventu — “prophecy from the event” — is the term for a passage written after what it appears to foretell. You will meet it constantly on this site, so it is worth being precise about it.
What the term means
A text presents itself as looking forward. On the dating argued by some scholars, it was in fact composed after the events it describes, and its accuracy is therefore the accuracy of a historian rather than of a seer. That is the claim. It is a claim about date of composition — nothing more and nothing less.
What it does not mean
It is not a synonym for forgery, and it is not an accusation of dishonesty. Writing in the voice of an earlier figure was a recognised literary convention in the ancient world, used by authors with no intention to deceive and read by audiences who understood the form. A scholar who argues that a passage is ex eventu is usually making a dating argument, not a moral one — and conflating the two is a good way to misrepresent an entire body of scholarship.
It is also not a verdict. On this site, “this passage may be ex eventu” is a position that goes into the case against, to be weighed. It is not a conclusion we reach by default because it sounds sober.
Why it is hard to test
The argument is often made from precision: a passage that is vague about distant events and suddenly specific about one particular period is said to reveal, by that change of texture, when its author was standing. It is a real observation and a genuinely useful one. It is also not a proof, for two reasons that pull in opposite directions.
First, the inference assumes that genuine prediction, if it occurred, would not be specific — which is an assumption about how prophecy works, not a finding about the text. Second, the same pattern is produced by ordinary editing: a text can be genuinely old and have been updated later, leaving precise passages inside an older frame. Distinguishing those two possibilities usually requires evidence from outside the passage, which is exactly what a dossier is for.
How we handle it
Where the ex eventu reading is the majority scholarly position, we say so, and the dossier will not carry grade 1. Where it is a minority position, we say that too, and it still appears in full in the case against. Where the evidence genuinely cannot separate the readings, the verdict is grade 3 — and the point of the page becomes showing the reader precisely what the disagreement turns on, rather than pretending to resolve it.