Including it only proves that it was not generated before a certain date. It can't prove that it was generated before something also generated after the headlin

Including it only proves that it was not generated before a certain date. It can't prove that it was generated before something also generated after the headline in question. You have to predict exactly what the headline is going to be though "On the Moon" is a fair guess but the chances you would get "Men walk on the moon" (plus "astronauts land on plain; collect rocks, plant flag" if we're using the subheadline too) exactly correct to fake it are really low. That's only possible on a very small number of dates where there's a known huge event coming up.