But the original question wasn't about ownership, it was about numbers. And without buying the discs (which I don't think many people here would do), we'd never know.
However, if there were additional books available through that route, then assuming they're in the public domain, they'd be usable here as well.
More than likely, though, it's just an attempt to pick up some cash with minimal effort, which means that the books came either from here or one of the other outlets where public domain books become available like the newsgroups.
Basically, unless you have a thriving business, you're not going to invest the money and time to scan additional books to distinguish yourself from larger, free sites. Or at least, that's the way to bet.