PG works based on US copyright law. And as I understand it that's also 70 years after author/translator death.
My gut feeling is that if anyone tried hard enough this ban could probably get lifted
That’s only the case for works published after the mid-70s. For works published before (which is all current PD books in the US), it’s 95 years after the date of publication, with a few exceptions where people failed to file renewal notices.