It would be interesting to know whether they have cleared these reprints with the Burroughs estate. The Tarzan name, for example, is a trademark, and trademarks (unlike copyright or patents) are forever. ERB, Inc. is apparently able to control new works using the Tarzan name/character, but I'm not sure about the status of an out-of-copyright text that includes the name in the title.

ERB, Inc. has been in the licensing biz for a long, long time, and their website's terms & conditions page suggests they know what they're doing--

Even reference works are not immune to the attentions of rights-holders and their lawyers--

BTW, even the Tarzan yell is trademarked:

So they've finally figured out a way of selling the squeal as well. . . .