[Alamo-Girl]

LOL! Ok, so maybe the paper won't tell them much - but microscopic things on the paper might tell them something. I don't know - but I strongly suspect the NSA knows a lot more than they are revealing and probably for good reason.

[Doctor Stochastic]

It's the FBI that does this stuff. NSA just listens. See Bamford's two books on them. Fiber analysis is commonly done. Of course, it may lead nowhere.

[Doctor Stochastic]

The envelopes are also subject to fiber analysis. Probably find out that they were produced for the Post Office.