But....now that you asked that, that is a GOOD question.
Why would a man who no longer had control over those papers have to designate somebody to look at them.
I could be wrong .. but I don't think just anyone can go in to see those documents
Though since they are from Clinton's term in office .. by him writing a letter gives Sandy and No Name (Bruce?) an excuse and cover
Probably because access to some of these docs is "need to know" and perhaps some like the presidential emails are still under some time limit where they are accessable only by Clinton's sig. In any case only Clinton would know who he needed to act on his behalf to research for Clinton's own testimony... so Bush couldn't pick Clinton's representative and do the designating. I suppose Clarke would have to designate a person to dig in the archives on his behalf as well.