I'd always thought that Arthur Ransome would be pretty politically correct (having married Trotsky's secretary), but at the denouement of his Swallows & Amazons novel "The Big Six" one of the characters uses a word that has now (in editions published after the author's death) become "negroes".
It is such a celebrated occurrence that it gets a
mention in that Wiki page.
It's worth noting that Ransome puts it into the mouth of one of the three working-class protagonists (Pete, of the
Death and Glories). Ransome probably thought that in 1940, when the book was written, middle-class children wouldn't use the word. Ransome's dialogue is quite well tuned to the different backgrounds of the children concerned.
I first read the book in the early 1960s (myself a working class boy in SE London), but even by then the usage stuck out as anachronistic.