Wikileaks wonderland

Genuine question: How do you know they are accurate?

You see, the problem I have with this leak and the previous one is reliability. May be someone can help me out. Do we know where all this information came from? Or are we assuming all information dumped on wikileaks is an original source? Pure fact or fact mixed with fiction?

Playing the devil's advocate here.... So far most wikileak files mentioned in the press seem to be "confirmations" of earlier speculations. It looks like what we suspected all along is true (however, we never saw it in writing, and writing makes it true somehow. And when it's on tv of course.....) An example:

Apparently one of the wikileak documents suggests there are nucleair weapons in The Netherlands. Information considered a public secret. This evening the foreign affairs minister was interviewed about this and he declined to comment. The journalist then said "well it's in the public domain anyway, look it's on wikileaks.". The minister still had no comments, but it would be easy to lure someone into a "oh well, you got me there! Yeah, we do have them. 50 to be precisely at Woensdrecht".

The fact that it's on wikileaks doesn't make it holy writ as such. By posting information "everybody knows already" (read: everybody suspects) there is a hint of familiarity. It must be true! Since there is an infodump at the moment, everybody dives into the content and not into the evidence itself. What about the nature of these documents. Again, are all these documents original sources?

If someone could explain to me how they all know these are original sources I'd be very grateful. I'm new to these wikileaks so I could have missed it.