DC has a good point and I agree.
The documents I saw on Wilson's website were scans of the actual post-ban approval letters signed by the head of ATF's Technology Department.
I had an interesting conversation with three ATF agents once. Only ONE of them knew what was legal and what was not. (Ah, your tax dollars at work.) If for some reason I was 'audited' by an agent like one of the inexperienced two, without a letter I could end up getting my rifle confiscated as a test case. With an ATF approved break I could show a copy of the letter and stay safe.
Unlikely? Yes, very unlikely, but I'm not going to be the test case for some green agent fresh out of school.