Trouble is, we have users from all over the world, and who knows the copyright laws in all those countries except the people who live in those countries? Most books there's no issue with (eg Dickens is out of copyright everywhere, AFAIK). It's really only 20th century authors that there may be issues with.
The best anyone can do in those circumstances is to say when the book was published, and when the author died, and let each downloader then make up their own mind whether or not it's "legit" for them to download that book.
Honestly, though, if a book is in any of the major public domain book collections, nobody going to get sued for putting in on a web server. It would be different if you downloaded "Gone With the Wind", and then started trying to sell it in the US, but nobody's going to be foolish enough to do that, I trust
. If a book is freely available, it's freely available - that's the practical situation. The most that any copyright holder is going to do, in cases where no money is changing hands, is request that it be removed and, as I said in an earlier message, Alex (the system owner) has a policy of immediately complying with such requests, so there's really no problem here.
"Don't ask, don't tell" is the best practical policy to follow. The books we upload here can all be legitimately downloaded by people in some part of the world or another.