Were Mondale and Dukakis Otherwise Engaged?

So Jimmy Carter, Al Gore, and John Kerry have all been added to the Democratic Convention speaker roster.  That's a reasonably impressive booking - fully 60% of the party's Presidential losers from the last 30 years.

The equivalent Republican field is limited to Bush 41 and Bob Dole, but so far as I know, the RNC hasn't managed to book either one for their convention.