I heard that topic being discussed on a talking head show once. They theorized that most of the recovered messages were indeed mirrored on the server of the other parties, and that many, many of them came from .gov servers from people conducting routine business, etc. concerning daily functions of their work so they were and are available on other servers... travel plans and details, protocol information, meeting notes, and other unclassified information flow from conducting their daily business.
The missing ones, they said, were likely not sinister at all... some were about chelsea's wedding and an awful lot of them were probably from blind servers without ping information readily available (such as no-response spam that most of us get that is passed directly to the spam folder without our even seeing it)
I am not a systems wonkie but I buy that explanation before I would buy the idea that there were 33,000 classified or otherwise significant documents shredded because of some nefarious interest; how would they know if there wasn't a mirror document on another system so how could they know which ones were "safe" to shred? But I guess people will believe what they want to believe without evidence. We spent millions to get actual evidence and all we got was the mugging sneer of Trey Gowdy, and an FBI director that seemed pretty professional to me.
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