In short, we really don't know, which is why we just ignore most of them outright. As you mention, Life+70 means that an entire creative team would need to die prior to 1945, unlikely for books even ten years earlier, not to mention "moral rights," which may never expire and the morbidity of hoping that a bunch of people are all dead.
There's a chance that some countries had pre-Life+70 laws whose works' terms didn't get extended retroactively, but nobody I've spoken to (admittedly no foreign Intellectual Property lawyers...) has investigated the issue beyond knowing that Britain did retroactively extend copyrights when they switched from Life+50 to Life+70 and some vagueness about Canadian copyrights that their Intellectual Property Office seemed to deny when I e-mailed them, though I may not have phrased the question in a manner that the clerk understood what I was going for and I never followed up.
