This has always been a problem and fire was a common enemy. You don't even have to go back as far as the 1800's. You can read about The 1973 Fire, National Personnel Records Center to get a basic idea of what kind of loss could occur and how they might go about reconstructing as much of that data as possible. Redundancy, indexing, backups, and disperate storage methods have always been important in data retention, still to this day.

I'd love to read a 'Salt' like book about your very question and will be eagerly watching this thread.