Williams got the theme credit, but a solo “music” credit (he was “Johnny” Williams back then) when he did the score, too. The others got screen credit when they did original scores, not when music was reused (such as Herrmann’s, which must have ticked him off—he flew into a rage when Jerry Goldsmith’s “Music by” credit appeared on a TV episode of something while Herrmann’s THEME music was playing).
I can picture Williams as an incredible prima donna. I’ve always thought he was overrated (including his Star Wars work.) I much prefer James Horner’s music.