I don't disagree, but it's definitely a minor one - if there's only one copy of a historically significant book in the world, I can't think of any better place

I don't disagree, but it's definitely a minor one - if there's only one copy of a historically significant book in the world, I can't think of any better place for it to be held than the Library of Congress. It's unlikely they've digitized it, though - I'm pretty sure the digitization effort there prioritizes the oldest books first, to make sure it gets done before they reach a condition that makes it impossible.