Dorchester is now trying to transfer rights back to authors, but they have a huge list of authors for whom they have no contact information. You may be on this list -- or you may know someone who is and could put them in touch with Dorchester. Here's what the publisher has to say:
Thank you for your support over the last 75 years.At this time, we are completing the reversion process, transferring all titles back to their respective authors. Though we have made great strides, our research has uncovered a number of authors for whom we have no contact information. In addition, there are a number of titles without corresponding authors. To complete this reversion process, we will need your help.
So check out Dorchester Publishing's full list of authors and titles. You just may be on that list.
Note: A lot of the authors are deceased, so agents and estates need to review this list as well.
(Thanks to @StaciaKane and @galleycat.)