I dont have a clue about what his publishers del was. My BIL is a well known riter who did NOT retain "All rights reserved by author" This is usually retined by cartoonists nd uthors with significcant illustrations (HOWARD PYLE and NC WYETH did not hqve any rights for their great art work in the pirate novels)
Sometimes, (and I think the early 20th century fits), the publishers tqke control of the entire work portfolio. The authors can always sign with new pubs but the pubs worked a lot closer then than now I hear. As I see, the later Tarzan books showed Tarzan's evolution and ERB was slowly getting his way.
I suppose, if you wish to see it all as a nail, No matter what I can dig up to the contrary, you will see this world via your hammer. I think you could have some great fun looking up in the U of Michigqns library system (U of Michigan is here most all PHd theses and disserttions come to reside in the"cloud"). Im sure theres a bunch of theses about this very question. Ive found blogs surrounding bith cmps and Ive also found that most of the combatants are quite respectful. They sound like this,
"Im not arguing, Im just trying to explain why youre wrong"--Now thats a nice way.
I think the evolution of Tarzan , as a literary fact, was probably a part of ERB' entire marketing plan for the series. Remember, it was the 1920's nd bit later.
Too bad ERB isnt alive so you could ask him whether he would class his early Tarzan books as written by a racist??