If you have the years handy, I can try a more rigorous issue-by-issue search. However, if they were all published pre-1950 and we trust Ockerbloom's "first renewals" list (I do, for at least a first pass), then they're public domain.
I'm guessing that Atlas went ahead because there's no trademark issue, not because of any copyright details. Nobody was going to confuse their title with the older series, so it's safe. As a modern parallel, I doubt even DC would give you more than a tiny bit of trouble if you published a comic titled "Resurrection Man," as long as it doesn't resemble their character.