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I can speculate from a 'school solution';
1. NYT got their FOIA request through, eventually, so the docs were out there. OSD does not necessarily think what they did was wrong.
2. Put the docs up on your web site. That way you can say, 'We've got nothing to hide and we're hiding nothing'.
3. Throw a lot of flak into the universe, to increase the noise-signal ratio.
The flak will be generated by legions of sympathetic RW bloggers, radio commentators, etc, who will dutifully comb through the docs as we have ... except with tendentious intent, cherry-picking proof of 'innocence' (or proof that it Just Doesn't Matter).
See also, David Kay WMD search data dump.
So why not post the docs?