ECHELON is probably the biggest (for tech) of the "oh, that couldn't be true" conspiracy theories that ended up being true. The whole release of information on it constitutes a big jolt to the head on what people will actually do.
I guess if you want to limit yourself to one delivery type. Its amazing how many old newspapers, transcripts of speeches & conversations, letters, and reports are available today that weren't in the past. Heck, scroll translations are also out there.
The world is an amazing place and people have written in many forms for a long time.