Huh, I didn't realize there was still discussion on this, and I can't recall what I've said on the matter (and don't feel like going through all the pages of the thread).
I am the one who stuffed the envelopes with the cards. I put several layers of security on these envelopes - not the least of which is this:
I didn't tell Banachek what kind of cards were being used in the test. I didn't say what brand, or what colour the backs were. In fact, I believe there were four different tests available (or was it three?), and the colours of the card backs were not the same for every one. I used red cards for some tests, and blue for others. Last I checked, the unopened tests were still at the JREF headquarters, and I imagine they can someday be opened for examination.
So not only did he not know the brand name of the cards, he also didn't know what colour they were, thereby making it impossible for him to have a deck of cards on his person for every possiblity - or, at least, incredibly unlikely.
In addition to this, there was tape across every edge and seam of every envelope, with my signature written across each piece of tape. It was impossible to remove without destroying the envelope, and I can verify that afterward they were all just as they were when I handed them over to the security officer.
And if I remember correctly (though now, looking back, I cannot be sure if it was for this test or another, so there's no sense in quoting me on this aspect), I put a secret mark on each envelope to ensure that, even if Banachek was a master forger and used entirely different envelopes that he had purchased himself, he would not know to replace the mark, having no idea that it was there in the first place.