I can't remember which show, but I remember watching a TV mystery with a picture of someone reading a newspaper as proof of someone being present on a certain day. Trouble was, the editor of the paper was in on the scam and ensured the headline would appear that day.
Another good source of fixed-in-the-past yet unpredictable data is the closing price of a collection of stocks from the previous day. This would make verification easier to automate.
You could (conceivably) make up plausible future stories, but not things like quarterly results, lawsuit outcomes, etc.