The English Collins first edition was partially rewritten for Putnam in America. On September 2, 1938, White wrote to David Garnett: "You were quite right about the Anthropophagi: I had always felt uncomfortable about them, and the American book club made me substitute 3 complete chapters about griffins, wyverns etc. for them, before they would take the book".
The version appearing in 1958 in the tetralogy was substantially revised, partly to incorporate events and themes that White had originally intended to cover in a fifth volume (which was finally published after his death, as The Book of Merlyn). To this end, the revised version includes several new episodes, including a pacifist passage in which Arthur is transformed into a wild goose that flies so high as to not be able to perceive national boundaries. It leaves out some of the episodes that had appeared in the original (notably Merlyn's battle with Madam Mim which appeared in the Disney film). Some critics considered the revised version to be inferior to the original.  Publishers have tended to carry on using the original versions when they were published independently of the tetralogy; the original, American, and "Once and Future King" versions are still in print.
The reasons White made the last revisions are open to speculation. The Sword in the Stone, although it includes some serious themes, is to some extent a rather whimsical fantasy of Merry England. Its connection with the classical Arthurian legend was actually rather limited, although what it did take from the Arthurian legend was accurate. It was awkward to treat this as the first part of a more serious treatment of the Arthurian legend. It is also possible that White felt in a darker mood after the Second World War. It has also been said that due to wartime censorship, the publishers did not want to print some of White's more strident anti-War sentiments (which are very prevalent in The Book of Merlyn).