Exactly.
Since the Netherlands is a member of the EU, it's a Life+70 country. Therefore, it's possible that the books are in the public domain only in the unlikely event that every contributor died prior to 1941.
However, if the system recognizes a "shortest term" rule, then the shorter US copyrights may be valid, putting them into the public domain for you. That is, unless the Netherlands recognizes GATT, also, which some countries use to restore the copyrights of people who fought in World War II, which Eisner did.
And it might be even more complicated.
I don't have anybody to ask about Dutch copyright law, unfortunately, so I can't help more than that. If you speak to a local lawyer, though, we'd love to hear what he has to say on the subject. We're trying to get a sense of what copyrights look like outside the United States for these purposes and the opposite (hosting non-US content here) with very little luck.