Science Fiction author Robert A. Heinlein (Stranger in a Strange Land, The Moon is a Harsh Mistress, etc) left his voluminous files to UC Santa Cruz -- with a stipulation that certain sections were to remain private and unexamined until 50 years after his death.

Sometimes I think people do that sort of thing to wait to unveil evidence of (let's say) animosity with other public figures until the person in question will be safely dead, but it's always fun to speculate on other possiblities.

For instance, maybe the queen always hated her job, but didn't want to say so. :)