BB also came out with authorized editions of ERB's Mars and Tarzan books. Ace published a few of them, but not the whole of each series. On the other hand ACE with great Frank Frazetta and Roy Kernkel covers ended up published most of ERB's other books, such as Venus and Pellucidar series, as well as the books not in any particular series (e.g. The Mad King, Beyond the Farthest Star).
The argument as been made that if ACE had not published LOTR, stirring up controversy, the series would not have made such a big splash in the 60s. Those of us who grew up in the 60s have to be thankful to both Ballantine and ACE's Donald Wolheim for publishing great science fiction and fantasy.