The US "just printed by date" rule won't be around forever: assuming no further changes in the US law, you'll have to start dealing with many of the same questions starting in 2019... and you'll STILL have a smaller public domain to play with.
Actually, when the US public domain begins to grow again in 2019, it will still be on a fixed-term system for a long time to come. No life+X copyrights were issued in the United States until January 1, 1978.
And you still have to do that for every single book; you can't batch- clear.
You have to do it for every single book under a life + system, too: you have to examine the book to see who the author is before you can refer to your list of death-dates. Of course, this is a silly argument to begin with, because regardless of the copyright regime, verifying public domain status is usually going to be a negligible effort compared to actually digitizing the book.
A American imprint without a date is in the public domain so long as you can prove it was printed before 1989. Go US!
I'm not certain that's a correct statement of the law. Are you?
It's not exactly a correct statement of the law, but you won't get into too much trouble following it. More correctly, before the effective date of the Berne Convention Implementation Act (March 1, 1989), if a book was published in the United States, by the authority of the copyright holder, and did not bear proper notice of copyright (which includes a date), it invalidated copyright in the work. Copyrights on works of foreign authors that lost copyright by this provision were restored on January 1, 1996, but the possession of a copy without the copyright notice, published before March 1, 1989, is usually enough to base an "innocent infringement" defense on. -- RS