I'm not sure about this case, but that's not always been true everywhere, historically. In the UK, at least, when books were extended to life + 70 that was retroactive for books originally published there. It was not retroactive in the USA, however (and more sensibly, I would say - whatever your views on term extension).
That's actually quite the oddity. It seems to go against conventional wisdom (but then when has the British Government done anything wise lately?) and copyright law itself in that once copyright lapses it is supposed to be non-ownable from that point on.
This has affected me and my business in the past - see http://blog.th.ingsmadeoutofotherthin.gs/eucalyptus-availabl... (halfway down, "A Note on Copyright" has an explanation of this oddity).