I think I rationalized the situation just like you, Matt. Why get a substitute when you could get the real thing? BTW, I also have the novelization of The Music Man.
I remember reading the novelization of West Side Story. Since I saw the film when it first came out (I was 12), the rape of Anita was somewhat stylized and it went over my head; not so in the paperback. Although not explicit, the sex scenes were a bit clearer to a young boy.
I had the great pleasure of seeing Ms. Nixon on stage in James Joyce's The Dead, a fascinating musical that sadly remained unrecorded. It was such a thrill to actually see the voice behind the screen, still sounding and looking lovely. Her legacy lives on. RIP.
The "forced" ending was not in the original play by Shaw, but was rewritten by the man himself for the screenplay of the 1938 film version. It was retained by Lerner for the Broadway production and for the 1964 film.
PMF beat me to it.