It is very likely that the copyright expired, and that the companies that reprinted the ACC were able to do so because the copyright expired. Today, copyrights last almost forever. But back in the day they lasted (I think) 28 years, and then could be renewed for another 28. But for books with rather limited distribution, most people didn't bother renewing. You can find out for sure through the Copyright Office. It might even be doable through their website.
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